GIS Glossary/G

GIS Glossary

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Gantt chart
A project management graph that displays tasks on a schedule, often used to plan and track projects. The Gantt chart was developed by the American mechanical engineer and management consultant Henry Laurence Gantt.

gateway
An OpenLS ArcWeb service that determines the location of wireless devices.

Gateway Service
An OpenLS ArcWeb service that determines the location of wireless devices.

Gaussian distribution
A theoretical frequency distribution of a dataset in which the distribution of values can be graphically represented as a symmetrical bell curve. Normal distributions are typically characterized by a clustering of values near the mean, with few values departing radically from the mean. There are as many values on the left side of the curve as on the right, so the mean and median values for the distribution are the same. Sixty-eight percent of the values are plus or minus one standard deviation from the mean; 95 percent of the values are plus or minus two standard deviations; and 99 percent of the values are plus or minus three standard deviations.

Gauss-Kruger projection
A projected coordinate system that uses the transverse Mercator projection to divide the world into standard zones 6 degrees wide. Used mainly in Europe and Asia, the Gauss-Krüger coordinate system is similar to the universal transverse Mercator coordinate system. The Gauss-Krüger projection is named for the German mathematician and scientist Karl Friedrich Gauss and the German geodesist and mathematician Johann Heinrich Louis Krüger.

gazetteer
A list of geographic place-names and their coordinates. Entries may include other information as well, such as area, population, or cultural statistics. Atlases often include gazetteers, which are used as indexes to their maps. Well-known digital gazetteers include the U.S. Geological Survey Geographic Names Information System (GNIS) and the Alexandria Digital Library Gazetteer.

GBF/DIME
Acronym for Geographic Base Files/Dual Independent Map Encoding. Vector geographic base files made for the 1970 and 1980 U.S. censuses, containing address ranges, ZIP Codes, and the coordinates of street segments and intersections for most metropolitan areas in the United States. TIGER files replaced DIME files for the 1990 and subsequent censuses.

GDB
A database or file structure used primarily to store, query, and manipulate spatial data. Geodatabases store geometry, a spatial reference system, attributes, and behavioral rules for data. Various types of geographic datasets can be collected within a geodatabase, including feature classes, attribute tables, raster datasets, network datasets, topologies, and many others. Geodatabases can be stored in IBM DB2, IBM Informix, Oracle, Microsoft Access, Microsoft SQL Server, and PostgreSQL relational database management systems, or in a system of files, such as a file geodatabase.

GDI
Acronym for Graphical Device Interface. A standard for displaying and transmitting text and graphical objects output devices, such as monitors and printers. GDI generally refers to the Windows GDI API.

generalization
The abstraction, reduction, and simplification of features for change of scale or resolution.

genetic algorithm
A search algorithm inspired by genetics and Darwin's theory of natural selection. The algorithm goes through an iterative process of applying genetic operators, such as reproduction, mutation, and crossover, to a collection of data over several stages. At each stage the fitness of the results is evaluated and the best of the results population is retained, until the results present an optimal solution.

geocentric
Measured from the earth or the earth's center.

geocentric coordinate system
A three-dimensional, earth-centered reference system in which locations are identified by their x-, y-, and z-values. The x-axis is in the equatorial plane and intersects the prime meridian (usually Greenwich). The y-axis is also in the equatorial plane; it lies at right angles to the x-axis and intersects the 90-degree meridian. The z-axis coincides with the polar axis and is positive toward the north pole. The origin is located at the center of the sphere or spheroid.

geocentric datum
A horizontal geodetic datum based on an ellipsoid that has its origin at the earth's center of mass. Examples are the World Geodetic System of 1984, the North American Datum of 1983, and the Geodetic Datum of Australia of 1994. The first uses the WGS84 ellipsoid; the latter two use the GRS80 ellipsoid. Geocentric datums are more compatible with satellite positioning systems, such as GPS, than are local datums.

geocentric latitude
The angle between the equatorial plane and a line from a point on the surface to the center of the sphere or spheroid. On a sphere, all lines of latitude are geocentric. Latitude generally refers to geodetic latitude.

geocentric longitude
The angle between the prime meridian and a line drawn from a point on the surface to the center of a sphere or spheroid. For an ellipsoid of revolution (such as the earth), geocentric longitude is the same as geodetic longitude.

geocloud
The term “cloud” represents the internet/web. Geocloud /Geocloud computing therefore is the ability for consumers, developers and applications to access computing resources from the cloud. These geographically aware/ spatial computing resources could be owned and operated by some third party provider – either for free or for a fee.

geocode
To assign a street address to a location.

geocoded feature class
A feature class created by batch geocoding.

GeocodeServer
An ArcGIS Server software component that provides programmatic access to an address locator and performs single and batch address matching. It is designed for use in building Web services and Web applications using ArcGIS Server.

geocoding
A GIS operation for converting street addresses into spatial data that can be displayed as features on a map, usually by referencing address information from a street segment data layer.

geocoding engine
An entity in the geocoding framework that drives the geocoding process.

geocoding index
An index on reference data used by an address locator to search for matching records in the reference data. A geocoding index is either a file or a database table containing index attributes used by the address locator.

geocoding platform
A conceptual entity of the geocoding framework that combines the interaction of the ArcGIS interface with the input parameters set in the address locator and the processes of the geocoding engine.

geocoding process
The steps involved in translating an address entry, searching for the address in the reference data embedded in an address locator, and delivering the best candidate or candidates. These steps include parsing the address, standardizing abbreviated values, assigning each address element to a category known as a match key, indexing the needed categories, searching the reference data, assigning a score to each potential candidate, filtering the list of candidates based on the minimum match score, and delivering the best match. The process requires reference files, input address records, address locators, and software.

geocoding reference data
Data that a geocoding service uses to determine the geometric representations for locations.

geocoding rule base
A collection of files that directs the geocoding engine in how to standardize address data and match it to the related location in the reference data. Each address locator style uses a specific rule base designed for that style.

geocoding service
In ArcGIS 8.3 and previous versions, an object that defines the process for translating nonspatial descriptions of places, such as street addresses, into spatial data that can be displayed as features on a map. A geocoding service defines the path to the reference data source and the file of nonspatial data, algorithms for standardizing addresses and matching them to the reference data, and parameters for reading address data, matching address data to the reference data, and creating output. In ArcGIS 9, a geocoding service is called an address locator.

geocoding style
A template on which a geocoding service is built. Each template is designed to accommodate a specific format of address and reference data, and geocoding parameters. Geocoding style template files have a .lot file extension.

geocomputation
The application of computer technology to spatial problems, including problems of collecting, storing, visualizing, and analyzing spatial data, and of modeling spatial system dynamics.

geodata
Information describing the location and attributes of things, including their shapes and representation. Geographic data is the composite of spatial data and attribute data.

geodatabase
A database or file structure used primarily to store, query, and manipulate spatial data. Geodatabases store geometry, a spatial reference system, attributes, and behavioral rules for data. Various types of geographic datasets can be collected within a geodatabase, including feature classes, attribute tables, raster datasets, network datasets, topologies, and many others. Geodatabases can be stored in IBM DB2, IBM Informix, Oracle, Microsoft Access, Microsoft SQL Server, and PostgreSQL relational database management systems, or in a system of files, such as a file geodatabase.

geodatabase data model
The schema for the various geographic datasets and tables in an instance of a geodatabase. The schema defines the GIS objects, rules, and relationships used to add GIS behavior and integrity to the datasets in a collection.

geodatabase feature dataset
In a geodatabase, a collection of feature classes stored together so they can participate in topological relationships with one another. All the feature classes in a feature dataset must share the same spatial reference; that is, they must have the same coordinate system and their features must fall within a common geographic area. Feature classes with different geometry types may be stored in a feature dataset. In ArcGIS, feature classes that participate in a geometric network must be placed in a feature dataset.

geodatabase replication
In ArcGIS, a method of distributing data across two or more geodatabases in order to synchronize data changes. An entire geodatabase or a subset of a geodatabase can be replicated. There are three types of geodatabase replication: two-way replication, one-way replication, and check-out replication.

GeoDataServer
In ArcGIS, a coarse-grained object that represents a geodatabase. It allows software users to perform replication operations, data extraction and database query operations on a geodatabase over the WAN using ArcGIS Server. Application developers can also use the GeoDataServer with geodatabase connections made over the LAN.

geodataset
Any organized collection of data in a geodatabase with a common theme.

geodesic
The shortest distance between two points on the surface of a spheroid. Any two points along a meridian form a geodesic.

geodesy
The science of measuring and representing the shape and size of the earth, and the study of its gravitational and magnetic fields.

geodetic datum
A datum that is the basis for calculating positions on the earth's surface or heights above or below the earth's surface.

geodetic latitude
The angle that a line drawn perpendicular to the surface through a point on a spheroid makes with the equatorial plane.

geodetic longitude
The angle between the plane of the meridian that passes through a point on the surface of the spheroid and the plane of a prime meridian, usually the Greenwich meridian.

Geodetic Reference System of 1980
The standard measurements of the earth's shape and size adopted by the International Union of Geodesy and Geophysics in 1979.

geodetic survey
A survey that takes the shape and size of the earth into account, used to precisely locate horizontal and vertical positions suitable for controlling other surveys.

geodetic 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.

geofence
A designated boundary around a geometry that, if crossed, initiates a notification. Geofences are often used in real-time route Web applications.

geographic
Of or relating to the earth.

geographic constraint
The minimum bounding rectangle (xmin, ymin and xmax, ymax) defined by coordinate pairs of a data source. All coordinates for the data source fall within this boundary.

geographic coordinate system
A reference system that uses latitude and longitude to define the locations of points on the surface of a sphere or spheroid. A geographic coordinate system definition includes a datum, prime meridian, and angular unit.

geographic coordinates
A measurement of a location on the earth's surface expressed in degrees of latitude and longitude.

geographic data
Information describing the location and attributes of things, including their shapes and representation. Geographic data is the composite of spatial data and attribute data.

geographic database
A database or file structure used primarily to store, query, and manipulate spatial data. Geodatabases store geometry, a spatial reference system, attributes, and behavioral rules for data. Various types of geographic datasets can be collected within a geodatabase, including feature classes, attribute tables, raster datasets, network datasets, topologies, and many others. Geodatabases can be stored in IBM DB2, IBM Informix, Oracle, Microsoft Access, Microsoft SQL Server, and PostgreSQL relational database management systems, or in a system of files, such as a file geodatabase.

geographic information science
The field of research that studies the theory and concepts that underpin GIS. It seeks to establish a theoretical basis for the technology and use of GIS, study how concepts from cognitive science and information science might apply to GIS, and investigate how GIS interacts with society.

geographic information system
An integrated collection of computer software and data used to view and manage information about geographic places, analyze spatial relationships, and model spatial processes. A GIS provides a framework for gathering and organizing spatial data and related information so that it can be displayed and analyzed.

geographic north
The direction from any point on the earth's surface to the geographic north pole.

geographic primitive
In MOLE, the most elementary part of a graphic. Icon, frame, and fill are examples of components that make up MOLE graphics.

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

geographic 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.

geography
The study of the earth's surface, encompassing the description and distribution of the various physical, biological, economic, and cultural features found on the earth and the interaction between those features.

geography level
A division of statistical geographic data, such as country, province, postal code, tract, or block group.

Geography Markup Language
An OpenGIS Implementation Specification designed to store and transport geographic information. GML is a profile (encoding) of XML.

geoid
A hypothetical surface representing the form the earth's oceans would take if there were no land and the water were free to respond to the earth's gravitational and centrifugal forces. The resulting geoid is irregular and varies from a perfect sphere by as much as 75 meters above and 100 meters below its surface.

geoid height
The height of the geoid above the ellipsoid.

geoid-ellipsoid separation
The distance from the surface of an ellipsoid to the surface of the geoid, measured along a line perpendicular to the ellipsoid. The separation is positive if the geoid lies above the ellipsoid, negative if it lies below.

geolocation
The process of creating geographic features from tabular data by matching the tabular data to a spatial location. An example of geolocation is creating point features from a table of x,y coordinate.

geometric coincidence
The distance within which features in a geometric network are deemed to be coincident and, therefore, connected.

geometric correction
The correction of errors in remotely sensed data, such as those caused by satellites or aircraft not staying at a constant altitude or by sensors deviating from the primary focus plane. Images are often compared to ground control points on accurate basemaps and resampled, so that exact locations and appropriate pixel values can be calculated.

geometric 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).

geometric effect
In ArcGIS, a dynamic process that can be applied within a representation rule to dynamically alter the geometry of features before they are drawn. Geometric effects can act on a single symbol layer, or on all symbol layers in a representation rule, and can be chained together to create cumulative effects.

geometric element
One of the most basic parts or components of a geometric figure: that is, a surface, shape, point, line, angle, or solid.

geometric network
Edge and junction features that represent a linear network, such as a utility or hydrologic system, in which the connectivity of features is based on their geometric coincidence. A geometric network does not contain information about the connectivity of features; this information is stored within a logical network. Geometric networks are typically used to model directed flow systems.

geometric transformation
The process of rectifying a raster dataset to map coordinates or converting a raster dataset from one coordinate system to another.

geometry
The measures and properties of points, lines, and surfaces. In a GIS, geometry is used to represent the spatial component of geographic features.

GeoMobility Server
An OpenLS platform for wireless Web services defined by the Open Geospatial Consortium.

geomorphology
The study of the nature and origin of landforms, including relationships to underlying structures and processes of formation.

geoprocessing
A GIS operation used to manipulate GIS data. A typical geoprocessing operation takes an input dataset, performs an operation on that dataset, and returns the result of the operation as an output dataset. Common geoprocessing operations include geographic feature overlay, feature selection and analysis, topology processing, raster processing, and data conversion. Geoprocessing allows for definition, management, and analysis of information used to form decisions.

geoprocessing server
A computer in a network that is used to handle geoprocessing tasks. Geoprocessing servers may use UNIX or Windows platforms, and include a utility to schedule remote processing.

geoprocessing settings
Any settings that affect working with or running tools. Geoprocessing settings include the state of the ArcToolbox window, the state of the Environment Settings dialog box, and variables that have been created at the command line. In ArcMap, geoprocessing settings are saved with a map document. In ArcCatalog, geoprocessing settings are persisted with the application.

geoprocessing tool
An ArcGIS tool that can create or modify spatial data, including analysis functions (overlay, buffer, slope), data management functions (add field, copy, rename), or data conversion functions.

GEOPUB30.DLL
An ArcView Geocoding Windows dynamic link library (DLL) for use on ArcView 3.x. It exposes additional geocoding requests by making them public (rather than private), Avenue scripts-callable requests.

georectification
The digital alignment of a satellite or aerial image with a map of the same area. In georectification, a number of corresponding control points, such as street intersections, are marked on both the image and the map. These locations become reference points in the subsequent processing of the image.

georeferencing
Aligning geographic data to a known coordinate system so it can be viewed, queried, and analyzed with other geographic data. Georeferencing may involve shifting, rotating, scaling, skewing, and in some cases warping, rubber sheeting, or orthorectifying the data.

georelational data model
A geographic data model that represents geographic features as an interrelated set of spatial and attribute data. The georelational model is the fundamental data model used in coverages.

GeoRSS
Acronym for Geographically Encoded Objects for RSS feeds. Metadata for RSS documents that describes the location of Web content.

geospatial data clearinghouse
A community of digital spatial data providers that maintain NSDI Clearinghouse Nodes as part of the U.S. National Spatial Data Infrastructure.

geospatial technology
A set of technological approaches, such as GIS, photogrammetry, and remote sensing, for acquiring and manipulating geographic data.

geospecific model
A model used to represent a real-world feature. For example, a geospecific model for the White House would look exactly like the White House and be used to represent the White House on a map of Washington, D.C.

geostationary
Positioned in an orbit above the earth's equator with an angular velocity the same as that of the earth and an inclination and eccentricity approaching zero. A geostationary satellite will orbit as fast as the earth rotates on its axis, so that it remains effectively stationary above a point on the equator. A geostationary satellite is geosynchronous, but geosynchronous satellites are not necessarily geostationary.

geostatistical layer file
A layer file created by the ArcGIS Geostatistical Analyst extension. It can be exported to ESRI GRID for further geoprocessing.

geostatistics
A class of statistics used to analyze and predict the values associated with spatial or spatio-temporal phenomena. Geostatistics provides a means of exploring spatial data and generating continuous surfaces from selected sampled data points.

geosurvey engine
The software module in Survey Analyst - Cadastral Editor that manages the interaction between cadastral fabric jobs and the cadastral fabric.

geosynchronous
Positioned in an orbit moving west to east with an orbital period equal to the earth's rotational period. If a satellite is in a geosynchronous orbit that is circular and lies in the equatorial plane, it is geostationary because it remains over one point on the equator. If not, the satellite appears to make a figure eight once a day between the latitudes that correspond to its angle of inclination over the equator.

geotypical model
A symbolic representation for a class of map features, such as government buildings. For example, on a map of the United States, a white building with a dome on top could be used as a geotypical model for all state capitols.

Get Report
An ArcWeb tool for ArcGIS that enables users to determine characteristics for a specified location and generate a report.

GIF
Acronym for Graphic Interchange Format. A low-resolution file format for image files, commonly used on the Internet. It is well-suited for images with sharp edges and reduced numbers of colors.

giomgr
In ArcSDE, a process that listens for client requests to connect to the database. When it receives such a request, it creates a connection by launching a gsrvr process dedicated to that client. The giomgr process is not used if the client makes a direct connection to the ArcSDE geodatabase.

GIS
Acronym for geographic information system. An integrated collection of computer software and data used to view and manage information about geographic places, analyze spatial relationships, and model spatial processes. A GIS provides a framework for gathering and organizing spatial data and related information so that it can be displayed and analyzed.

GIS coordinate
In Survey Analyst for field measurements, the single coordinate for a survey point that is the best overall representation for that survey point's location, defined by one or more projects. Feature geometry is always linked to the GIS coordinate.

GIS Data ReViewer
An application used to manage data quality control, visually check data and run batch checks for attribute and geometry defects. Defects are recorded in an error table that can be used to resolve errors and verify corrections.

GIS server
The components of ArcGIS Server that host and run services. A GIS server consists of a server object manager and one or more server object containers.

GIScience
Abbreviation for geographic information science. The field of research that studies the theory and concepts that underpin GIS. It seeks to establish a theoretical basis for the technology and use of GIS, study how concepts from cognitive science and information science might apply to GIS, and investigate how GIS interacts with society.

global analysis
The computation of an output raster where the output value at each cell location may be a function of all the cells in the input raster.

Global Check method
In Survey Analyst for field measurements, one of two ways to apply the Coordinate Out of Tolerance command. The Global Check method searches for coordinates out of tolerance within the whole survey dataset.

global functions
The computation of an output raster where the output value at each cell location may be a function of all the cells in the input raster.

global mode
A navigation mode in ArcGlobe during which the camera target is always at the center of the globe.

Global Navigation Satellite System
The Russian counterpart of the United States Global Positioning System.

global polynomial interpolation
In ArcGIS Geostatistical Analyst, a deterministic interpolation method. The interpolated surface is not required to conform to the sample data points, and the method does not have standard errors associated with it.

Global Positioning System
A system of radio-emitting and -receiving satellites used for determining positions on the earth. The orbiting satellites transmit signals that allow a GPS receiver anywhere on earth to calculate its own location through trilateration. Developed and operated by the U.S. Department of Defense, the system is used in navigation, mapping, surveying, and other applications in which precise positioning is necessary.

global spatial data infrastructure
A global framework of technologies, policies, standards, and human resources necessary to acquire, process, store, distribute, and improve the use of geospatial data across multiple countries and organizations.

GlobalID
A field of type UUID (Universal Unique Identifier) in which values are automatically assigned by the geodatabase when a row is created. The GlobalID field is necessary for maintaining object uniqueness across replicas. All feature classes and tables participating in one-way or two-way replication must contain the GlobalID field. This field is not editable and is automatically populated when it is added for existing data.

globally unique identifier
A string used to uniquely identify an interface, class, type library, component category, or record.

globe
A sphere on which a map of the earth or a celestial body is represented. Since the earth's natural shape is similar to a sphere, globes distort the earth's features far less than flat maps.

globe document
A disk-based representation of the globe view or views contained in ArcGlobe. Globe documents have a .3dd extension.

globe properties
In ArcGlobe, properties that can be set for a globe document. These include vertical exaggeration, background color, or sun position.

globe terrain
In ArcGlobe, a globe surface with base heights supplied from an elevation layer.

globe view
In ArcGlobe, the display window in which a globe can be viewed.

GLONASS
Acronym for Global Navigation Satellite System. The Russian counterpart of the United States Global Positioning System.

Glue
A Java-based toolkit for accessing SOAP Web services. Glue is developed by webMethods.

glyph
The geometric shape of a character in a font.

GML
Acronym for Geography Markup Language</I>. An OpenGIS Implementation Specification designed to store and transport geographic information. GML is a profile (encoding) of XML.

GMT
The time at the prime meridian, which runs through the Royal Observatory in Greenwich, England. From 1884 to 1928, Greenwich mean time was the official name (and is still the popular name) for universal time. It sometimes also refers to coordinated universal time.

gnomonic projection
A planar projection, tangent to the earth at one point, projected from the center of the globe. All great circles appear as straight lines on this projection, so that the shortest distance between two points is a straight line. The gnomonic projection is useful in navigation. The gnomonic projection was used by Thales of Miletus, an ancient Greek astronomer and philosopher, to chart the heavens. It is possibly the oldest map projection.

gon
A unit of angular measurement in which the angle of a full circle is 400 gradians and a right angle is 100 gradians. The common abbreviation for gradian is grad.

goodness of fit
In modeling, the degree to which a model predicts observed data; a measure of predictive power.

gore
A map, shaped like the area between a pair of parentheses, of an area that lies between two lines of longitude. A gore can be fitted to the surface of a globe with little distortion.

GPS
Acronym for Global Positioning System</I>. A system of radio-emitting and -receiving satellites used for determining positions on the earth. The orbiting satellites transmit signals that allow a GPS receiver anywhere on earth to calculate its own location through trilateration. Developed and operated by the U.S. Department of Defense, the system is used in navigation, mapping, surveying, and other applications in which precise positioning is necessary.

grad
A unit of angular measurement in which the angle of a full circle is 400 gradians and a right angle is 100 gradians. The common abbreviation for gradian is grad.

gradian
A unit of angular measurement in which the angle of a full circle is 400 gradians and a right angle is 100 gradians. The common abbreviation for gradian is grad.

gradient
The ratio between vertical distance (rise) and horizontal distance (run), often expressed as a percentage. A 10-percent gradient rises 10 feet for every 100 feet of horizontal distance.

gradient of gravity
The direction of the maximum increase in gravity in a horizontal plane.

graduated color map
A map on which a range of colors indicates a progression of numeric values. For example, increases in population density might be represented by the increased saturation of a single color, or temperature differences by a sequence of colors from blue to red.

graduated symbol map
A map with symbols that change in size according to the value of the attribute they represent. For example, denser populations might be represented by larger dots, or larger rivers by thicker lines.

grain tolerance
In ArcInfo Workstation, a parameter controlling the number of vertices and the distance between them on lines that represent curves. The smaller the grain tolerance, the closer the vertices can be. Unlike densify tolerance, grain tolerance can affect the shape of curves.

granularity
The coarseness or resolution of data. Granularity describes the clarity and detail of data during its capture and visualization.

graph
A map used to plot a course for air or water navigation.

graphic
An image produced by and stored in a computer as data for display.

graphic component
In MOLE, the most elementary part of a graphic. Icon, frame, and fill are examples of components that make up MOLE graphics.

graphic text
Text added in ArcMap layout view that exists in page space and is stored in a map document. Graphic text does not move if the extent or scale is changed.

Graphical Device Interface
A standard for displaying and transmitting text and graphical objects output devices, such as monitors and printers. GDI generally refers to the Windows GDI API.

graphical user interface
A software display of program options that allows a user to choose commands by pointing to icons, dialog boxes, and lists of menu items on the screen, typically using a mouse. This contrasts with a command line interface in which control is accomplished via the exchange of strings of text.

graticule
A network of longitude and latitude lines on a map or chart that relates points on a map to their true locations on the earth.

graticule alignment of labels
A label positioning method in which labels are oriented along the graticule of the data frame. This is useful for maps of large areas, for cartographic or stylistic reasons.

gravimeter
A device used to measure small variations in the earth's gravitational field between two or more points.

gravimetric geodesy
The science of deducing the size and shape of the earth by measuring its gravitational field.

gravity model
A model that assumes that the influence of phenomena or populations on each other varies inversely with the distance between them.

gray scale
All the shades of gray from white to black.

great circle
Any circle or near circle produced by the intersection of the surface of a sphere and a flat plane that passes through the center of the sphere. The equator and all lines of longitude are great circles. Great circles are used in navigation, since the shortest path between any two points on the earth's surface lies on a great circle.

Greenwich mean time
The time at the prime meridian, which runs through the Royal Observatory in Greenwich, England. From 1884 to 1928, Greenwich mean time was the official name (and is still the popular name) for universal time. It sometimes also refers to coordinated universal time.

Greenwich meridian
The meridian adopted by international agreement in 1884 as the prime meridian, the 0-degree meridian from which all other longitudes are calculated. The Greenwich prime meridian runs through the Royal Observatory in Greenwich, England.

grid
In cartography, any network of parallel and perpendicular lines superimposed on a map and used for reference. These grids are usually referred to by the map projection or coordinate system they represent, such as universal transverse Mercator grid.

grid cell
The smallest unit of information in raster data, usually square in shape. In a map or GIS dataset, each cell represents a portion of the earth, such as a square meter or square mile, and usually has an attribute value associated with it, such as soil type or vegetation class.

grid meridian
In Survey Analyst for field measurements, any meridian that is parallel to the central meridian, used when computing points in planar rectangular coordinate systems of limited extent.

grid north
The direction north along the north-south grid lines of a map projection.

grid stack
A mechanism for storing multivariate raster data in ESRI software, consisting of an ordered set of spatially overlapping grids (referred to as layers) referenced by an INFO file or geodatabase. A stack is treated as a single entity for multivariate analysis. Cluster analysis, classification, and principal component analysis all work on the layers in a stack.

ground control
A system of points with known positions, elevations, or both, used as fixed references in georeferencing map features, aerial photographs, or remotely sensed images.

ground control point
An accurately surveyed coordinate location for a physical feature that can be identified on the ground. Control points are used in least-squares adjustments as the basis for improving the spatial accuracy of all other points to which they are connected.

ground receiving station
Communications equipment for receiving and transmitting signals to and from satellites such as Landsat.

ground truth
The accuracy of remotely sensed or mathematically calculated data based on data actually measured in the field.

group
A collection of ArcWeb Services users who share the same activation code. Group members can transfer credits and share data.

group administrator
The person who sets permissions for the members of an ArcWeb Services group and who is usually the chief contact for the organization.

group layer
A group of several layers that appear and act as a single layer. Group layers make it easier to organize a map, assign advanced drawing order options, and share layers for use in other maps.

GRS80
Acronym for Geodetic Reference System of 1980</I>. The standard measurements of the earth's shape and size adopted by the International Union of Geodesy and Geophysics in 1979.

GSDI
Acronym for global spatial data infrastructure</I>. A global framework of technologies, policies, standards, and human resources necessary to acquire, process, store, distribute, and improve the use of geospatial data across multiple countries and organizations.

gsrvr
A process that connects to a relational database management system (RDBMS), using the RDBMS server libraries, and becomes the dedicated link for a GIS client to the database. A gsrvr process is only used in three-tiered geodatabase connections. The GIS client sends instructional commands to the gsrvr process on how to build appropriate SQL statements to perform the requested spatial action (pan, zoom, and so on).

GUI
Acronym for graphical user interface</I>. A software display of program options that allows a user to choose commands by pointing to icons, dialog boxes, and lists of menu items on the screen, typically using a mouse. This contrasts with a command line interface in which control is accomplished via the exchange of strings of text.

GUID
Acronym for globally unique identifier</I>. A string used to uniquely identify an interface, class, type library, component category, or record.