GIS Glossary/D

GIS Glossary

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daemon
In programming, a process that continuously runs in the background, without being explicitly implemented, and performs a specified operation at predefined times or in response to certain events. Daemon is a UNIX term; the Windows equivalent is a system agent or service.

dangle
The endpoint of a dangling arc.

dangle length
In ArcInfo coverages, the minimum length allowed for dangling arcs by the clean process, which removes dangling arcs shorter than the dangle tolerance.

dangle tolerance
In ArcInfo coverages, the minimum length allowed for dangling arcs by the clean process, which removes dangling arcs shorter than the dangle tolerance.

dangling arc
An arc having the same polygon on both its left and right sides and having at least one node that does not connect to any other arc. It often occurs where a polygon does not close properly, where arcs do not connect properly (an undershoot), or where an arc was digitized past its intersection with another arc (an overshoot). A dangling arc is not always an error; for example, it can represent a cul-de-sac in a street network.

dangling node
The endpoint of a dangling arc.

dasymetric mapping
A technique in which attribute data that is organized by a large or arbitrary area unit is more accurately distributed within that unit by the overlay of geographic boundaries that exclude, restrict, or confine the attribute in question. For example, a population attribute organized by census tract might be more accurately distributed by the overlay of water bodies, vacant land, and other land-use boundaries within which it is reasonable to infer that people do not live.

data
Any collection of related facts arranged in a particular format; often, the basic elements of information that are produced, stored, or processed by a computer.

data capture
Any operation that converts GIS data into computer-readable form. Geographic data can be captured by being downloaded directly into a GIS from sources such as remote-sensing or GPS data, or it can be digitized, scanned, or keyed in manually from paper maps or photographs.

data change message
In ArcGIS, a message containing any inserts, updates, and deletes applied to a replica. These messages are used to synchronize replicas in a disconnected environment.

data conversion
The process of translating data from one format to another.

data definition language
A set of SQL statements that can be used either interactively or within a programming language to create a new database, set permissions on it, and define its attributes.

data dictionary
A catalog or table containing information about the datasets stored in a database. In a GIS, a data dictionary might contain the full names of attributes, meanings of codes, scale of source data, accuracy of locations, and map projections used.

data element
The smallest unit of information used to describe a particular characteristic of a spatial dataset. A data element is a logically primitive description that cannot be further subdivided.

data file
A file that holds text, graphics, or numbers.

data format
The structure used to store a computer file or record.

data frame
A map element that defines a geographic extent, a page extent, a coordinate system, and other display properties for one or more layers in ArcMap. A dataset can be represented in one or more data frames. In data view, only one data frame is displayed at a time; in layout view, all a map's data frames are displayed at the same time. Many cartography texts use the term "map body" to refer to what ESRI calls a data frame.

data integration
The process of sharing and combining data between two organizations or systems.

data integrity
The degree to which the data in a database is accurate and consistent according to data model and data type.

data logger
A lightweight, handheld field computer used to store data collected by a GPS receiver.

Data Manager Web Service
A SOAP ArcWeb service that allows users to upload their own point, line, or polygon data and attribute information to use in custom map and spatial query data sources.

data message
Information in a satellite's GPS signal that reports its orbital position, operating health, and clock corrections.

data model
In GIS, a mathematical construct for representing geographic objects or surfaces as data. For example, the vector data model represents geography as collections of points, lines, and polygons; the raster data model represents geography as cell matrixes that store numeric values; and the TIN data model represents geography as sets of contiguous, nonoverlapping triangles.

data product
In ArcWeb Services, a collection of layers that has a single credit cost. Every data layer has an associated data product.

data recorder
A lightweight, handheld field computer used to store data collected by a GPS receiver.

data repository
A repository structure, physical or virtual, that collects, stores, and disseminates information, metadata, and data. A clearinghouse provides widespread access to information and is generally thought of as reaching or existing outside organizational boundaries.

data sharing
Making data available and accessible to organizations or individuals other than the creator of the data.

data source
Any data. Data sources may include coverages, shapefiles, rasters, or feature classes.

data structure
The organization of data within a specific computer system that allows the data to be stored and manipulated effectively; a representation of a data model in computer form.

data synchronization
The process of applying data changes from a replica to the relative replica in a replica pair. Data changes include row or feature inserts, updates, and deletes. Synchronization can be performed in one or both directions between a replica pair.

data transfer
The process of moving data from one system to another or from one point on a network to another.

data type
The attribute of a variable, field, or column in a table that determines the kind of data it can store. Common data types include character, integer, decimal, single, double, and string.

data view
An all-purpose view in ArcMap and ArcReader for exploring, displaying, and querying geographic data. This view hides all map elements, such as titles, north arrows, and scale bars.

database
One or more structured sets of persistent data, managed and stored as a unit and generally associated with software to update and query the data. A simple database might be a single file with many records, each of which references the same set of fields. A GIS database includes data about the spatial locations and shapes of geographic features recorded as points, lines, areas, pixels, grid cells, or TINs, as well as their attributes.

database administrator
The person who manages a database. Database administration includes user setup, security, backup and recovery procedures for data, and optimization of physical data storage for best performance.

database connection
A link to a database from a software application. Database connections have two states: connected to or disconnected from the database. Deletion of a database connection only deletes the connection itself, not the database or its contents. Creation of a database connection requires selection of a data provider for data retrieval.

database design
The development of the conceptual, logical, and physical structures of a database in order to meet user requirements.

database generalization
The abstraction, reduction, and simplification of features and feature classes for deriving a simpler model of reality or decreasing stored data volumes.

database management system
A set of software applications used to create and maintain databases according to a schema. Database management systems provide tools for adding, storing, changing, deleting, and retrieving data.

database role
The database permissions category assigned to a group of users who perform the same types of tasks and, therefore, require the same level of database access. Database roles are used by database administrators to simplify the administration of user privileges.

database statistics
Mathematically calculated data that describes the state of a database and which the database management system (DBMS) uses to optimize query response.

database support
The proprietary database platforms supported by a program or component.

data-driven ring analysis
A type of market analysis primarily used to look at competing sites or to select potential new locations.

dataflow
The route of data passage through a system.

dataset
Any collection of related data, usually grouped or stored together.

dataset precision
The mathematical exactness or detail with which a value is stored within a dataset, based on the number of significant digits that can be stored for each coordinate.

datasnooping
In Survey Analyst, the process of testing each measurement using the W-test.

datum
The reference specifications of a measurement system, usually a system of coordinate positions on a surface (a horizontal datum) or heights above or below a surface (a vertical datum).

datum level
A surface to which heights, elevations, or depths are referenced.

datum plane
A surface to which heights, elevations, or depths are referenced.

datum points
In Survey Analyst for field measurements, survey points that are not defined by computations, but that are the input data for the initial computations in a sequence of computations.

datum shift
A systematic conversion of the latitude-longitude values for a set of points from one geographic coordinate system to equivalent values in another geographic coordinate system. Depending on the geographic coordinate systems involved, the transformation can be accomplished in various ways. Typically, equations are used to model the position and orientation of the "from" and "to" geographic coordinate systems in three-dimensional coordinate space; the transformation parameters may include translation, rotation, and scaling. Other methods, including one used in transformations between NAD 1927 and NAD 1983, use files in which the differences between the two geographic coordinate systems are given for a set of coordinates; the values of other points are interpolated from these.

datum transformation
A systematic conversion of the latitude-longitude values for a set of points from one geographic coordinate system to equivalent values in another geographic coordinate system. Depending on the geographic coordinate systems involved, the transformation can be accomplished in various ways. Typically, equations are used to model the position and orientation of the "from" and "to" geographic coordinate systems in three-dimensional coordinate space; the transformation parameters may include translation, rotation, and scaling. Other methods, including one used in transformations between NAD 1927 and NAD 1983, use files in which the differences between the two geographic coordinate systems are given for a set of coordinates; the values of other points are interpolated from these.

dbf
A database file format. In the ArcWeb Services Web site, users can upload data into Builder as either a DBF file or a shapefile (SHP).

DBF file
A database file format. In the ArcWeb Services Web site, users can upload data into Builder as either a DBF file or a shapefile (SHP).

DBMS
A set of software applications used to create and maintain databases according to a schema. Database management systems provide tools for adding, storing, changing, deleting, and retrieving data.

DCOM
Acronym for Distributed Component Object Model. Extends COM to support communication among objects on different computers on a network.

DDL
A set of SQL statements that can be used either interactively or within a programming language to create a new database, set permissions on it, and define its attributes.

dead reckoning
A navigation method of last resort that uses the most recently recorded position of a ship or aircraft, along with its speed and drift, to calculate a new position.

debug
To test for, detect, and correct errors in a computer program or component.

decimal degrees
Values of latitude and longitude expressed in decimal format rather than in degrees, minutes, and seconds.

decision support system
A computer program that includes data presentation and modeling tools that help people understand problems and find solutions.

declination
In a spherical coordinate system, the angle between the equatorial plane and a line to a point somewhere on the sphere.

deeply stateful application
An application that uses the GIS server to maintain application state by changing the state of a server object or its related objects. Deeply stateful applications require nonpooled server objects.

default cadastral fabric
In Survey Analyst - Cadastral Editor, the most up-to-date version of the cadastral fabric in the database that corresponds to the default version in the database. The default cadastral fabric does not represent the current legal state of the cadastral fabric.

default interface
When a COM object is created, the interface that is returned automatically if no other interface is specified. Most ArcObjects classes specify IUnknown as the default interface.

default junction type
In geometric networks, the user-established junction type that automatically connects two edges in the absence of a current user choice. An edge may also have a default end junction type, used for the free ends of new edges.

default style
The original style that is used to symbolize a layer class in ArcWeb Services. Symbols can be overwritten in a map data source.

defined study area
A study area with a defined boundary, such as a city.

definition query
In ArcMap, a request that examines feature or tabular attributes based on user-selected criteria and displays only those features or records that satisfy the criteria.

deflection
The creation of a segment at an angle relative to an existing segment.

degree
A unit of angular measure represented by the symbol &#176;. The earth is divided into 360 degrees of longitude and 180 degrees of latitude.

degree slope
One method for representing the measurement of an inclined surface. The steepness of a slope may be measured from 0 to 90 degrees.

degrees-minutes-seconds
The unit of measure for describing latitude and longitude. A degree is 1/360th of a circle. A degree is further divided into 60 minutes, and a minute is divided into 60 seconds.

Delaunay triangles
The components of Delaunay triangulation. Delaunay triangles cannot exist alone; they must exist as part of a set or collection that is typically referred to as a triangulated irregular network (TIN). A circle circumscribed through the three nodes of a Delaunay triangle will not contain any other points from the collection in its interior.

Delaunay triangulation
A technique for creating a mesh of contiguous, nonoverlapping triangles from a dataset of points. Each triangle's circumscribing circle contains no points from the dataset in its interior. Delaunay triangulation is named for the Russian mathematician Boris Nikolaevich Delaunay.

deletes table
The geodatabase system table, created when a feature class or table is registered as versioned, that maintains information on all rows that have been deleted or updated.

delimiter
A character, such as a space or comma, that separates words or values.

delta database
A file that contains data edits that can be exchanged between geodatabases or between geodatabases and other data stores. The edits can come from a checkout geodatabase, modified rows between source and target versions, or a custom application. Supported delta file formats are XML (delta XML file) and delta database (.mdb file).

delta file
A file that contains data edits that can be exchanged between geodatabases or between geodatabases and other data stores. The edits can come from a checkout geodatabase, modified rows between source and target versions, or a custom application. Supported delta file formats are XML (delta XML file) and delta database (.mdb file).

delta table
One of two geodatabase system tables&#8212;the adds and deletes tables&#8212;created for a feature class or table when it is registered as versioned. These tables record changes made to a version during editing.

DEM
Acronym for digital elevation model. The representation of continuous elevation values over a topographic surface by a regular array of z-values, referenced to a common datum. DEMs are typically used to represent terrain relief.

demographics
The statistical characteristics (such as age, birth rate, and income) of a human population.

demography
The statistical study of human populations, especially their locations, distribution, economic statistics, and vital statistics.

densify
To add vertices to a line at specified distances without altering the line's shape.

densitometer
An instrument for measuring the opacity of translucent materials such as photographic negatives and optical filters.

density
In spatial measurements, the quantity per unit area or length.

density slicing
A technique normally applied to a single-band monochrome image for highlighting areas that appear to be uniform in tone, but are not. Grayscale values (0-255) are converted into a series of intervals, or slices, and different colors are assigned to each slice. Density slicing is often used to highlight variations in vegetation.

dependent variable
The variable representing the process being predicted or modeled, such as crime, foreclosure, or rainfall. The dependent variable is a function of the independent variables. Regression can be used to predict the dependent variable, using known (observed) values to build (calibrate) the regression model. In the regression equation, the dependent variable appears on the left side of the equal sign.

deployment
The installation of a component or application on a target machine.

depot
In ArcGIS Network Analyst, a network location used to represent a starting, stopping, or renewal location for routes in vehicle routing problem (VRP) analysis. Users can specify multiple depots. Depots are used as locations for loading/unloading vehicles within the fleet.

depot visit
In ArcGIS Network Analyst, an object used to represent a single visit to a specific depot in vehicle routing problem (VRP) analysis. A depot visit may occur at the start of a route, the end of the route, or as a renewal midway along a route.

depression contour
On a topographic map, concentric contour lines drawn with hachures to indicate a closed depression or basin. Concentric contour lines drawn without hachure marks indicate a hill.

depth contour
A line on a map connecting points of equal depth below a hydrographic datum.

depth curve
A line on a map connecting points of equal depth below a hydrographic datum.

derived data
In ModelBuilder, data created by running a geoprocessing operation on existing data. Derived data from one process can serve as input data for another process.

derived value
In ModelBuilder, data created by running a geoprocessing operation on existing data. Derived data from one process can serve as input data for another process.

descending node
The point at which a satellite traveling north to south crosses the equator.

descriptive data
Tabular or textual data describing the geographic characteristics of features.

descriptor
A type of attribute for network elements that cannot be apportioned. The value of a descriptor stays the same through the length of an edge element in a network dataset. Descriptors describe characteristics of the element; for example, the number of lanes for a particular road in a road network.

designated market area
A television market as defined by Nielsen Media Research. Most DMAs correspond to whole counties, but there are a few exceptions where counties are split into different DMAs.

desire-line analysis
A type of market analysis that draws lines from a set of geocoded points (usually customers) to a single, central point (usually a store). Desire lines can be weighted.

desktop GIS
Mapping software that is installed onto and runs on a personal computer and allows users to display, query, update, and analyze data about geographic locations and the information linked to those locations.

destination
The secondary object in a relationship class, such as a table containing attributes associated with features in a related table.

destination table
In ArcView 3.x, one of the two tables involved in a join operation. The destination table must be the active table; the attributes of the source (inactive) table are appended to it.

Detail page
One of two types of pages in the Survey Analyst Survey Explorer. The Detail page displays a detailed view of individual survey objects.

determinate flow direction
A conclusively definitive line or course in which something is issuing or moving in a stream. For an edge feature, this occurs when the flow direction can be ascertained from the connectivity of a network, the locations of sources and sinks, and the enabled or disabled states of features.

deterministic model
In spatial modeling, a type of model or a part of a model in which the outcome is completely and exactly known based on known input; the fixed or nonrandom components of a spatial model. The spline and inverse distance weighted interpolation methods are deterministic since they have no random components. The kriging and cokriging interpolation methods may have a deterministic component, often called the trend.

detrending
The process of removing the trend from a spatial model by subtracting the trend surface (usually polynomial functions of the spatial x- and y-coordinates) from the original data values. The resulting detrended values are called residuals.

developable surface
A geometric shape such as a cone, cylinder, or plane that can be flattened without being distorted. Many map projections are classified in terms of these shapes.

developer product
Products that can be used on one machine, similar to single use products. Each developer product requires a unique registration number used to generate the authorization file. The Software Authorization Wizard is then used to enter the authorization file and unlock the software for use.

developer sample
A sample contained in the ArcGIS Developer Help system.

development environment
A software product used to write, compile, and debug components or applications.

device context
Represents a surface that can be drawn to, for example, a screen, bitmap, or printer. In ArcGIS, the Display abstract class is used to abstract a device context.

device coordinates
The coordinates shown on a digitizer or display, as opposed to those of a recognized datum or coordinate system.

DGIWG
Acronym for Digital Geographic Information Working Group. A group established in 1983 to develop standards for spatial data exchange among nations participating in the North Atlantic Treaty Organization (NATO). The goals of the group are interoperability and burden sharing among nations, and its membership has recently expanded beyond NATO nations. While DGIWG is not an official NATO body, its work on standards has been recognized by the NATO Geographic Conference (NGC).

DGPS
A technique for increasing the accuracy of GPS measurements by comparing the readings to two receivers&#8212;one roving and the other a fixed base station&#8212;and a known location.

DHTML
An extension to HTML that allows Web designers to make elements on a Web page interactive, rather than changeable only when the page is loaded.

dialog box
In geoprocessing, a form consisting of a tool's parameters.

diazo process
A way of quickly and inexpensively copying maps using a diazo compound, ultraviolet light, and ammonia.

difference image
In image processing, an image made by subtracting the pixel values of one image from those in another.

differential correction
A technique for increasing the accuracy of GPS measurements by comparing the readings to two receivers&#8212;one roving and the other a fixed base station&#8212;and a known location.

differential Global Positioning System
A technique for increasing the accuracy of GPS measurements by comparing the readings to two receivers&#8212;one roving and the other a fixed base station&#8212;and a known location.

diffusion
The spread of an innovation or technology use among a group of people or organizations.

DIGEST
Acronym for Digital Geographic Information Exchange Standard. A standard for spatial data transfer among nations, data producers, and data users. The Digital Geographic Information Working Group (DGIWG) developed the standard to support interoperability within and between nations and share the burden of digital data production. The standard addresses the exchange of raster, matrix, and vector data (and associated text) and a range of levels of topological structures.

digital
Represented in discrete, quantified units rather than continuously. Computers process and store information in digital form.

digital elevation model
The representation of continuous elevation values over a topographic surface by a regular array of z-values, referenced to a common datum. DEMs are typically used to represent terrain relief.

Digital Geographic Information Exchange Standard
A standard for spatial data transfer among nations, data producers, and data users. The Digital Geographic Information Working Group (DGIWG) developed the standard to support interoperability within and between nations and share the burden of digital data production. The standard addresses the exchange of raster, matrix, and vector data (and associated text) and a range of levels of topological structures.

Digital Geographic Information Working Group
A group established in 1983 to develop standards for spatial data exchange among nations participating in the North Atlantic Treaty Organization (NATO). The goals of the group are interoperability and burden sharing among nations, and its membership has recently expanded beyond NATO nations. While DGIWG is not an official NATO body, its work on standards has been recognized by the NATO Geographic Conference (NGC).

digital image
An image stored in binary form and divided into a matrix of pixels. Each pixel consists of a digital value of one or more bits, defined by the bit depth. The digital value may represent, but is not limited to, energy, brightness, color, intensity, sound, elevation, or a classified value derived through image processing. A digital image is stored as a raster and may contain one or more bands.

digital image processing
Any technique that changes the digital values of an image for the sake of analysis or enhanced display, such as density slicing or low- and high-pass filtering.

digital line graph
Data files containing vector representations of cartographic information derived from USGS maps and related sources. DLGs include information from the USGS planimetric map base categories such as transportation, hydrography, contours, and public land survey boundaries.

digital nautical chart
A nautical database developed from existing hard-copy charts, digital data, bathymetric survey information, imagery, and various raster data. DNCs are used by the U.S. military and its allies for marine navigation.

digital number
In a digital image, a value assigned to a pixel.

digital orthophoto quadrangle
A computer-generated, uniform-scale image created from an aerial photograph. Digital orthophoto quadrangles are true photographic maps in which the effects of tilt and relief are removed by a mathematical process called transformation or rectification. The uniform scale of a DOQ allows accurate measurement of distances.

digital orthophoto quarter quadrangle
A digital orthophoto quadrangle (DOQ) divided into four quadrants.

digital raster graphic
A raster image of a scanned USGS standard series topographic map, usually including the original border information, referred to as the map collar, map surround, or marginalia. Source maps are georeferenced to the surface of the earth, fit to the universal transverse Mercator (UTM) projection, and scanned at a minimum resolution of 250 dpi. The accuracy and datum of a DRG matches the accuracy and datum of the source map.

digital terrain elevation data
A format for elevation data, usually tiled in 1-degree cells, produced by the National Geospatial-Intelligence Agency and U.S. allies for military applications.

digital terrain model
The representation of continuous elevation values over a topographic surface by a regular array of z-values, referenced to a common datum. DEMs are typically used to represent terrain relief.

digitizer
A device connected to a computer, consisting of a tablet and a handheld puck, that converts positions on the tablet surface as they are traced by an operator to digital x,y coordinates, yielding vector data consisting of points, lines, and polygons.

digitizing
The process of converting the geographic features on an analog map into digital format using a digitizing tablet, or digitizer, which is connected to a computer. Features on a paper map are traced with a digitizer puck, a device similar to a mouse, and the x,y coordinates of these features are automatically recorded and stored as spatial data.

digitizing mode
A way of using a digitizing tablet in which locations on the tablet are mapped to specific locations on the screen. Moving the digitizer puck on the tablet surface causes the screen pointer to move to precisely the same position on the screen.

Dijkstra's algorithm
An algorithm that examines the connectivity of a network to find the shortest path between two points. Dijkstra's algorithm is named after the Dutch computer scientist Edsger Dijkstra (1930-2002).

dilution of precision
An indicator of satellite geometry for a constellation of satellites used to determine a position. Positions with a lower DOP value generally constitute better measurement results than those with higher DOP. Factors determining the total GDOP (geometric DOP) for a set of satellites include PDOP (positional DOP), HDOP (horizontal DOP), VDOP (vertical DOP), and TDOP (time DOP).

DIME
Acronym for Dual Independent Map Encoding. A data storage format for geographic data developed by the U.S. Census Bureau in the 1960s. DIME-encoded data was stored in Geographic Base Files (GBF). The Census Bureau replaced the DIME format with Topologically Integrated Geocoding and Referencing (TIGER) in 1990.

dimension
A length of a certain distance and bearing.

dimension construction method
One of a number of procedures that dictate what type of dimension feature is created and the number of points required to complete the feature's geometry. Construction methods include simple aligned, aligned, linear, rotated linear, free aligned, and free linear.

dimension feature
In ArcMap, a special kind of geodatabase annotation that shows specific lengths or distances on a map. A dimension feature may indicate the length of a side of a building or land parcel, or it may indicate the distance between two features, such as a fire hydrant and the corner of a building.

dimension feature class
A geodatabase feature class that stores dimension features.

dimension style
Description of a dimension feature's symbology, what parts of it are drawn, and how it is drawn. Every time a new dimension feature is created, it is assigned a particular style according to its shared characteristics. A collection of dimension styles is associated with a dimension feature class. Styles for a dimension feature class are created, copied, and managed using ArcCatalog or the editing capabilities in ArcMap. Styles are then assigned to individual dimension features.

Dimensioning toolbar
A toolbar in ArcMap that facilitates the creation of dimension features.

DIP
Any technique that changes the digital values of an image for the sake of analysis or enhanced display, such as density slicing or low- and high-pass filtering.

direct connect
An ArcSDE connection that results in a two-tier configuration, in which the ArcSDE client application communicates directly with the database.

directed link
In ArcInfo Workstation, an arc between two nodes with one direction specified.

directed network flow
A network state in which edges have an associated direction of flow. In a directed network flow, the resource that traverses a network's components cannot choose a direction to take, as in hydrologic and utility systems.

direction
In an ArcGIS vertical coordinate system, an identifier that indicates whether z-values are positive up or positive down. Heights or elevations are usually positive up, against the force of gravity (indicated by +1). Depths are usually positive down, with the force of gravity (indicated by -1).

direction field
In Survey Analyst for field measurements, a field in the computation page that allows the entry of bearings or azimuths between an input survey point and a computed survey point.

directional filter
In image processing, an edge-detection filter that enhances those linear features in an image that are oriented in a particular direction.

directional influences
Natural or physical processes that affect a measured trait or attribute so that the magnitude of the effects on the attribute vary in different directions.

directory
An area of a computer disk that holds a set of data files, other directories, or both. Operating systems use directories to organize data. Directories are arranged in a tree structure, in which each branch is a subdirectory of its parent branch. The location of a directory is specified with a path&#8212;for example, C:\gisprojects\shrinkinglemurhabitatgrids.

Directory Service
An OpenLS ArcWeb service used to find points of interest and other entities around a given location.

Dirichlet tessellation
A partition of space into areas, or cells, that surround a set of geometric objects (usually points). These cells, or polygons, must satisfy the criteria for Delaunay triangles. All locations within an area are closer to the object it surrounds than to any other object in the set. Voronoi diagrams are often used to delineate areas of influence around geographic features. Voronoi diagrams are named for the Ukrainian mathematician Georgy Fedoseevich Voronoi (1868-1908).

dirty areas
Regions surrounding features that have been altered after the initial topology validation process and require additional topology validation to be performed to find any errors.

disabled feature
In geometric networks, an object or shape representing a geographic object through which flow is impossible.

disconnected editing
The process of copying data to another geodatabase, editing that data, then merging the changes with the data in the source or master geodatabase.

discrete data
Data that represents phenomena with distinct boundaries. Property lines and streets are examples of discrete data.

discrete digitizing
A method of digitizing in which points are placed individually to define a feature's shape.

discrete feature
A feature that has definite feature boundaries.

discrete raster
A raster that typically represents phenomena that have clear boundaries with attributes that are descriptions, classes, or categories. Generally, integers are used for the cell values. In a raster of land cover, for example, the value 1 might represent forestland, the value 2 urban land, and so on. It is assumed that the phenomena that each value represents fill the entire area of the cell. Rasters representing land use, political boundaries or ownership are examples of discrete rasters.

disk
A storage medium for recording digital information, consisting of a round, flat, spinning plate coated with a magnetic material.

disk cache
In ArcGlobe, the folder on a computer's disk drive where ArcGlobe stores layer cache files.

DispID binding
A type of early binding in which DispID properties and methods are accessed at compile time, so there's no need to call them at run time. DispID binding is used for components that have type libraries but don't support vTable binding. MapObjects uses DispID binding.

displacement link
In ArcGIS, a link created to define the source and destination coordinates for a spatial adjustment. Links are represented as arrows with the arrowhead pointing toward the destination location. Links can be created manually or loaded from a link file.

displacement vector
In Survey Analyst - Cadastral Editor, the difference in the coordinates of a point between successive least-squares adjustments. A set of displacement vectors is recorded for a point when the point is part of a least-squares adjustment. Adjustment vectors can be used to track spatial changes in the cadastral fabric over time, and to adjust associated feature classes to match the most up to date cadastral fabric location.

display
Often used to refer to subclasses of the Display abstract class. For example, "when drawing to the display" means when drawing to any of the display coclasses; "the display pipeline" refers to the sequence of calls made when drawing occurs.

display projection
The coordinate system used for displaying geographic data. Examples include the data frame in ArcMap and the view in ArcView GIS.

display scale
The scale at which data is rendered on a computer screen or on a printed map.

display type
The mode of command representation on a computer screen. The display type controls whether you see a command's image, its caption, or both when it appears on a toolbar or in a menu.

display unit
The unit of measure used to render dimensions of shapes, distance tolerances, and offsets on a computer screen or on a printed map. Although they are stored with consistent units in the dataset, users can choose the units in which coordinates and measurements are displayed&#8212;for example, feet, miles, meters, or kilometers.

dissemination
The spread of an innovation or technology use among a group of people or organizations.

dissolve
A geoprocessing command that removes boundaries between adjacent polygons that have the same value for a specified attribute.

dissolve route events
In linear referencing, a procedure that combines event records in tables where there are events on the same route that have the same value for specified fields. The Dissolve Route Events tool combines events when there is measure overlap, and is available for both line and point event tables.

distance
The measure of separation between two entities or locations that may or may not be connected, such as two points. Distance is differentiated from length, which implies a physical connection between entities or locations.

distance decay
A mathematical representation of the effect of distance on the accessibility of locations and the number of interactions between them, reflecting the notion that demand drops as distance increases. Distance decay can be expressed as a power function or as an exponential function.

distance field
In the Survey Analyst for field measurements Survey Explorer, a field for entering distance for use in a computation.

distance unit
The unit of measurement for distance, such as feet, miles, meters, and kilometers.

distortion
On a map or image, the misrepresentation of shape, area, distance, or direction of or between geographic features when compared to their true measurements on the curved surface of the earth.

distortion circle
A graphical representation of the spatial distortion at a particular map location. The indicatrix is the figure that results when a circle on the earth's surface is plotted to the corresponding point on a map. The shape, size, and orientation of an indicatrix at any given point depend on the map projection used. In conformal (shape-preserving) projections, the indicatrix is a circle; in nonconformal projections, it is an ellipse at most locations. As a visual aid, indicatrices convey a general impression of distortion; as mathematical tools, they can be used to quantify distortion of scale and angle precisely. The indicatrix is named for Nicolas Auguste Tissot, the French mathematician who developed it.

Distributed Component Object Model
Extends COM to support communication among objects on different computers on a network.

distributed data
Data spread over multiple platforms or a network by a process referred to as replication.

distributed database
A database with records that are dispersed between two or more physical locations. Data distribution allows two or more people to be working on the same data in separate locations.

distribution
The frequency or amount at which a thing or things occur within a given area.

dithering
The approximation of shades of gray or colors in a computer image made by arranging pixels of black and white or other colors in alternate layers. The technique gives the appearance of a wider range of color or shades than is actually present in the image. It is widely used to improve the appearance of images displayed on devices with limited color palettes.

diurnal
Daily, as in the revolution of the earth.

diurnal arc
The apparent path from rise to set made by a heavenly body across the sky.

DLG
Acronym for digital line graph. Data files containing vector representations of cartographic information derived from USGS maps and related sources. DLGs include information from the USGS planimetric map base categories such as transportation, hydrography, contours, and public land survey boundaries.

DLL
Acronym for dynamic-link library. A type of file that stores shared code to be used by multiple programs (a "code library"). Programs access the shared code by linking to the DLL file when they run, a process referred to as dynamic linking. The DLL file must be registered for other programs to locate it.

DMA
Acronym for Designated Market Area</I>. A television market as defined by Nielsen Media Research. Most DMAs correspond to whole counties, but there are a few exceptions where counties are split into different DMAs.

DMS
The unit of measure for describing latitude and longitude. A degree is 1/360th of a circle. A degree is further divided into 60 minutes, and a minute is divided into 60 seconds.

DNC
Acronym for digital nautical chart</I>. A nautical database developed from existing hard-copy charts, digital data, bathymetric survey information, imagery, and various raster data. DNCs are used by the U.S. military and its allies for marine navigation.

DNS
Acronym for domain name system</I>. The Internet distributed system that stores IP addresses and domain names to assist with the routing of network traffic.

dockable window
A window that can exist in a floating state or be attached to the main application window.

docking
Moving a floating toolbar or window to a fixed location in the graphical user interface.

document
A component of an ArcView 3.x project. Each document type (view, table, chart, layout, script) has its own window and interface.

documentation
Supporting information for software data and tools. Documentation may be descriptive or instructional, and is published in a variety of formats, including user's guides and manuals, desktop help systems, embedded or context-sensitive help, tutorials, reports, and metadata.

Documentation Editor
In geoprocessing, the interface used to write documentation for tools, toolsets, toolboxes, and processes within a model.

domain
The range of valid values for a particular metadata element.

domain name
The unique name of a computer system on the Internet, such as "esri.com."

domain name system
The Internet distributed system that stores IP addresses and domain names to assist with the routing of network traffic.

dongle
A small hardware device that provides the unique number used in the generation of a license file. The key is plugged into either the parallel or USB port on the License Manager Server. UNIX users of ArcGIS software do not need a hardware key. Hardware keys are also called dongles.

donut rings
A method of defining the rings in an analysis so that the values inside the rings are exclusive. For example, in an analysis with three donut rings and 10 households in each, the total number of households for each ring would be 10.

DOP
Acronym for dilution of precision</I>. An indicator of satellite geometry for a constellation of satellites used to determine a position. Positions with a lower DOP value generally constitute better measurement results than those with higher DOP. Factors determining the total GDOP (geometric DOP) for a set of satellites include PDOP (positional DOP), HDOP (horizontal DOP), VDOP (vertical DOP), and TDOP (time DOP).

Doppler shift
The apparent change in frequency of sound or light waves caused by the relative motion between a source and an observer. As they approach one another, the frequency increases; as they draw apart, the frequency decreases. The Doppler shift is also known as the Doppler effect, and is named for Austrian physicist and mathematician Christian Andreas Doppler.

Doppler-aided GPS
Signal processing that uses a measured Doppler shift to help the receiver track the GPS signal.

DOQ
Acronym for digital orthophoto quadrangle</I>. A computer-generated, uniform-scale image created from an aerial photograph. Digital orthophoto quadrangles are true photographic maps in which the effects of tilt and relief are removed by a mathematical process called transformation or rectification. The uniform scale of a DOQ allows accurate measurement of distances.

DOQQ
Acronym for digital orthophoto quarter quadrangle</I>. A digital orthophoto quadrangle (DOQ) divided into four quadrants.

dot density map
A quantitative, thematic map on which dots of the same size are randomly placed in proportion to a numeric attribute associated with an area. Dot density maps convey the intensity of an attribute.

dot distribution map
A map that uses dots or other symbols to represent the presence, quantity, or value of a phenomenon or thing in a specific area. In a dot distribution map, the size of the dots is scaled in proportion to the intensity of the variable.

dot screen
A photographic film covered with uniformly sized, evenly spaced dots used to break up a solid color, producing an apparently lighter color.

dots per inch
A measure of the resolution of scanners, printers, and graphic displays. The more dots per inch, the more detail can be displayed in an image.

double precision
The level of coordinate exactness based on the possible number of significant digits that can be stored for each coordinate. Datasets can be stored in either single or double precision. Double-precision geometries store up to 15 significant digits per coordinate (typically 13 to 14 significant digits), retaining the accuracy of much less than 1 meter at a global extent.

double-coordinate precision
The level of coordinate exactness based on the possible number of significant digits that can be stored for each coordinate. Datasets can be stored in either single or double precision. Double-precision geometries store up to 15 significant digits per coordinate (typically 13 to 14 significant digits), retaining the accuracy of much less than 1 meter at a global extent.

Douglas-Peucker algorithm
An algorithm that simplifies complex lines by reducing the number of points used to represent them. The Douglas-Peucker algorithm was developed by the Canadian geographers David H. Douglas and Thomas K. Peucker.

downstream
In network tracing, the direction along a line or edge that is the same as the direction of flow.

dpi
Acronym for dots per inch</I>. A measure of the resolution of scanners, printers, and graphic displays. The more dots per inch, the more detail can be displayed in an image.

drafting
A method of drawing with pencil or pen and ink, used in cartographic reproduction.

drainage
All map features associated with the movement and flow of water, such as rivers, streams, and lakes.

draped layer
A layer in ArcGlobe that has been categorized to be draped on top of the globe surface.

draping
A perspective or panoramic rendering of a two-dimensional image superimposed onto a three-dimensional surface. For example, an aerial photograph might be draped over a digital elevation model (DEM) to create a realistic terrain visualization.

drawing priority
In 3D analysis, the order in which layers that occupy the same x,y,z positions are drawn in a scene. For example, if a road feature layer and an orthophoto are draped over the same terrain model, the roads and raster may appear patchy or broken up where they coincide. The drawing priority for the raster can be reduced so it will appear below the features. The drawing priority can only be changed for polygon features and surfaces.

DRG
Acronym for digital raster graphic</I>. A raster image of a scanned USGS standard series topographic map, usually including the original border information, referred to as the map collar, map surround, or marginalia. Source maps are georeferenced to the surface of the earth, fit to the universal transverse Mercator (UTM) projection, and scanned at a minimum resolution of 250 dpi. The accuracy and datum of a DRG matches the accuracy and datum of the source map.

drift
The general pattern of z-values throughout a kriging model. The drift, or structure, forms the model's basic shape.

drive-time area
A zone around a map feature measured in units of time needed for travel by car. For example, a store's 10-minute drive-time area defines the area in which drivers can reach the store in 10 minutes or less.

drum scanner
A type of scanner in which a hard-copy image or map is attached to a cylinder that spins while a sensor captures a digital image from the surface of the page.

DTD
Acronym for document type definition</I>. A set of rules that define the allowed structure and properties of XML documents.

DTED
Acronym for digital terrain elevation data</I>. A format for elevation data, usually tiled in 1-degree cells, produced by the National Geospatial-Intelligence Agency and U.S. allies for military applications.

DTM
Acronym for digital elevation model</I>. The representation of continuous elevation values over a topographic surface by a regular array of z-values, referenced to a common datum. DEMs are typically used to represent terrain relief.

Dual Independent Map Encoding
A data storage format for geographic data developed by the U.S. Census Bureau in the 1960s. DIME-encoded data was stored in Geographic Base Files (GBF). The Census Bureau replaced the DIME format with Topologically Integrated Geocoding and Referencing (TIGER) in 1990.

duplicate labels
Labels with identical content. Maplex for ArcGIS provides the option of labeling only a single feature out of a cluster of similar features. Identical labels will not be placed within the user-defined distance of a placed label.

dynamic binding
A COM technique that an application uses for determining an object's properties and methods at run time, rather than when the code is compiled. Late binding is generally used by scripting languages.

dynamic feature class
A feature class consisting of points associated with address elements in an address data table that change based on changes made to the address data table.

dynamic HTML
An extension to HTML that allows Web designers to make elements on a Web page interactive, rather than changeable only when the page is loaded.

dynamic segmentation
The process of computing the map locations of linearly referenced data (for example, attributes stored in a table) at run time so they can be displayed on a map, queried, and analyzed using a GIS. The dynamic segmentation process enables multiple sets of attributes to be associated with any portion of a line feature without segmenting the underlying feature. In the transportation field, examples of such linearly referenced data might include accident sites, road quality, and traffic volume.

dynamic style
In ArcWeb Services, a map style that changes based on the selected style sheet. Users can select from a set of defined dynamic styles for a map data source, but they cannot create dynamic styles.

dynamic-link library
A type of file that stores shared code to be used by multiple programs (a "code library"). Programs access the shared code by linking to the DLL file when they run, a process referred to as dynamic linking. The DLL file must be registered for other programs to locate it.