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GIS Glossary

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In ArcScene or ArcGlobe, the backdrop of the view. The color of the background can be set to suggest sky, empty space, or any color that improves visualization.

background image

A satellite image, aerial photograph, or scanned map over which vector data is displayed. Although a background image can be used to align coordinates, it is not linked to attribute information and is not part of the spatial analysis in a GIS.


Electromagnetic energy that is reflected back toward its source by terrain or particles in the atmosphere.


A copy of a file, a set of files, or a disk for safekeeping in case the original is lost or damaged.


Acronym for best available map. The most suitable data source for a map.


A set of adjacent wavelengths or frequencies with a common characteristic. For example, visible light is one band of the electromagnetic spectrum, which also includes radio, gamma, and infrared waves.

band ratio

A digital image-processing technique that enhances contrast between features by dividing a measure of reflectance for the pixels in one image band by the measure of reflectance for the pixels in the other image band.

band separate

An image format that stores each band of data in a separate file.

band-pass filter

A wave filter that allows signals in a certain frequency to pass through, while blocking or attenuating signals at other frequencies.


The amount of digital data that can be transferred over a computer network within a specified time period, usually measured in bits per second (bps).

bar scale

A map element used to graphically represent the scale of a map. A scale bar is typically a line marked like a ruler in units proportional to the map's scale.


In network analysis, an entity that prevents flow from traversing a network edge or junction.

base data

Map data over which other, thematic information is placed.

base height

In aerial photography, the height or altitude from which a photograph is taken.

base height ratio

In aerial photography, the distance on the ground between the centers of overlapping photos, divided by aircraft altitude. In a stereomodel, base height ratio is used to determine vertical exaggeration.

base layer

A data layer in a GIS to which all other layers are geometrically referenced.

base station

A GPS receiver at a known location that broadcasts and collects correction information for roving GPS receivers.

base symbol

In ArcGIS Tracking Analyst, the default symbol used to represent an event or a feature on a map.

base table

In a geodatabase, the spatially-enabled DBMS table that holds the main attribute values of a dataset. A business table with a spatial column is a feature class, and a business table with a raster column is a raster dataset or a raster catalog. In the database, the business table name is the dataset name.

base tag

A text formatting tag that allows control of how the ESRI Maplex Labeling Engine places labels based on multiple fields relative to a feature. The field identified with the base tag is placed nearest the feature, and other fields are placed relative to the position of the base field.


An accurately surveyed line from which other lines or the angles between them are measured.


A map depicting background reference information such as landforms, roads, landmarks, and political boundaries, onto which other thematic information is placed. A basemap is used for locational reference and often includes a geodetic control network as part of its structure.

batch file

A text file containing commands that is sent to the CPU to be executed automatically. A batch file allows the central processing unit (CPU) to process the commands at off-peak times or at a regularly scheduled time, rather than on demand from the user.

batch geocoding

The process of geocoding many address records at the same time.

batch mode operation

A procedure which uses a given ArcToolbox tool to process a set of information, or batch, rather than applying the tool to one piece at a time. Batch mode operation is available through tools in ArcGIS 8.3 and previous versions.

batch processing

A method for processing data automatically in which the data is grouped into batches and executed by the computer at one time, without user interaction.

batch table

In ArcToolbox, a table which displays the input name, user-selected parameters, and output name, where applicable, for all entries pertaining to a group, or batch, of jobs. Batch tables are available through tools in ArcGIS 8.3 and previous versions.

batch vectorization

An automated process that converts raster data into vector features for an entire raster or a portion of it based on user-defined settings.

bathymetric curve

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

bathymetric map

A map representing the topography of a seafloor or lake bed, using contour lines to indicate depth.


The science of measuring and charting the depths of water bodies to determine the topography of a lake bed or seafloor.

battle dimension

In MOLE, the primary area in which a force unit operates, such as air, space, ground, sea, surface, and subsurface.

battleships grid

A grid of numbered rows and lettered columns (or vice versa) superimposed on a map, used to find and identify features. Alphanumeric grids are commonly used as a reference system on local street maps.

baud rate

In communications, the number of electrical cycles, or signals, transmitted per second. At lower transfer speeds the baud rate equals the data transfer rate measured in bps, or bits per second. Baud rate and bps are still sometimes used interchangeably, though inaccurately, since current standards allow for the encoding of multiple bits into a single cycle.

Bayes' theorem

A theorem developed by English mathematician Thomas Bayes (1702-1761) about conditional probability. It states that the probability of a given event, given the original data and some new data, is proportional to the probability of the event given the original data only, and the probability of the new data given the original data and the event.

Bayesian statistics

A statistical approach to measuring likelihood. Bayesian estimates are based on the synthesis of a prior distribution and current sample data. Classical approaches to statistics estimate the probability of an event by averaging all possible data. The Bayesian approach, in contrast, weights probability according to actual data from a particular situation. It also factors in data from sources outside the statistical investigation, such as past experience, expert opinion, or prior belief. This outside information is described by a distribution that includes all possible values for the parameter.


The horizontal direction of a point in relation to another point, expressed as an angle from a known direction, usually north, and usually measured from 0 degrees at the reference direction clockwise through 360 degrees. Bearings are often referred to as true bearings, magnetic bearings, or assumed bearings, depending on whether the meridian is true, magnetic, or assumed.

bearing method

In Survey Analyst for field measurements, one of two methods for computing the coordinate geometry traverse. The bearing method uses compass directions for the orientation of each course.


The actions or characteristics exhibited by an object in a database, as defined by a set of rule.


A brass or bronze disk, set in a concrete base or similarly permanent structure, inscribed with a mark showing its elevation above or below an adopted vertical datum.

best available map

The most suitable data source for a map.

best route

The route of least impedance between two or more locations, taking into account connectivity and travel restrictions such as one-way streets and rush-hour traffic.

Bezier curve

A curved line whose shape is derived mathematically rather than by a series of connected vertices. In graphics programs, a Bézier curve usually has two endpoints and two handles that can be moved to change the direction and the steepness of the curve. Bézier curves are named for the French engineer Pierre Bézier (1910-1999).

Bhattacharyya distance

In digital image processing, a measure of the theoretical distance between two normal distributions of spectral classes, which acts as an upper limit on the probability of error in a Bayesian estimate of correct classification. Bhattacharyya distance is named for the Indian mathematician Anil Kumar Bhattacharyya (1915–1996).

big endian

A computer hardware architecture in which, within a multibyte numeric representation, the most significant byte has the lowest address and the remaining bytes are encoded in decreasing order of significance.

bilinear interpolation

A resampling method that uses a weighted average of the four nearest cells to determine a new cell value.


A method for displaying graphics associated with features in a three-dimensional map display by posting them vertically as two-dimensional symbols and orienting them to always face the user.


In a variogram map, each cell that groups lags with similar distance and direction. Bins are commonly formed by dividing the sample area into a grid of cells or sectors, and are used to calculate the empirical semivariogram for kriging.


In computing, having only two states, such as yes or no, on or off, true or false, or 0 or 1.

binary file

A file that contains data encoded as a sequence of bits (ones and zeros) instead of plain text. A binary file, such as a DLL or an executable file, contains information that can be directly loaded or executed by a computer.

binary large object

A large block of data, such as an image, a sound file, or geometry, stored in a database. The database cannot read the BLOB's structure and only references it by its size and location.


In computer programming, the process by which a program discovers an object's methods and properties.

bingo grid

A grid of numbered rows and lettered columns (or vice versa) superimposed on a map, used to find and identify features. Alphanumeric grids are commonly used as a reference system on local street maps.

binomial distribution

A distribution describing the probability of obtaining exactly K successes in N independent trials, where each trial results in either a success or a failure.


The study of the geographical distribution of living things.


The total amount of organic matter in a defined area; usually refers to vegetation.


The smallest unit of information within a computer. A bit can have one of two values, 1 and 0, that can represent on and off, yes and no, or true and false.

bit depth

The range of values that a particular raster format can store, based on the formula 2n. An 8-bit depth dataset can store 256 unique values.


An image format in which one or more bits represent each pixel on the screen. The number of bits per pixel determines the shades of gray or number of colors that a bitmap can represent.

blind digitizing

A method of manual digitizing in which the operator has no graphic display on hand with which to see the digitized coordinates as they are captured.


Acronym for binary large object. A large block of data, such as an image, a sound file, or geometry, stored in a database. The database cannot read the BLOB's structure and only references it by its size and location.


In ArcGIS, a group of records in a compressed file geodatabase feature class or table that are stored together. The arrangement of compressed data into blocks helps optimize query performance.

block attribute

In CAD, a collection of objects that can be associated to form a single object.

block group

A unit of U.S. census geography that is a combination of census blocks. A block group is the smallest unit for which the U.S. Census Bureau reports a full range of demographic statistics. There are about 700 residents per block group. A block group is a subdivision of a census tract.

block kriging

A kriging method in which the average expected value in an area around an unsampled point is generated rather than the estimated exact value of an unsampled point. Block kriging is commonly used to provide better variance estimates and smooth interpolated results.


In ArcGIS, a geocoding indexing process that reduces the number of potential matches that need to be checked.


In surveying, a defective measurement that can be detected by a statistical test.


In ArcWeb Services, a shortcut that saves the current map view, including extents, active layers, and styles for future use.

Boolean expression

An expression, named for the English mathematician George Boole (1815-1864), that results in a true or false (logical) condition. For example, in the Boolean expression "HEIGHT > 70 AND DIAMETER = 100," all locations where the height is greater than 70 and the diameter is equal to 100 would be given a value of 1, or true, and all locations where this criteria is not met would be given a value of 0, or false.

Boolean operation

A GIS operation that uses Boolean operators to combine input datasets into a single output dataset.

Boolean operator

A logical operator used in the formulation of a Boolean expression. Common Boolean operators include AND, which specifies a combination of conditions (A and B must be true); OR, which specifies a list of alternative conditions (A or B must be true); NOT, which negates a condition (A but not B must be true); and XOR (exclusive or), which makes conditions mutually exclusive (A or B may be true but not both A and B).

border arcs

The arcs that create the boundary line of a polygon coverage.


A line separating adjacent political entities, such as countries or districts; adjacent tracts of privately-owned land, such as parcels; or adjacent geographic zones, such as ecosystems. A boundary is a line that may or may not follow physical features, such as rivers, mountains, or walls.

boundary effect

A problem created during spatial analysis, caused by arbitrary or discrete boundaries being imposed on spatial data representing nondiscrete or unbounded spatial phenomena. Boundary problems include edge effects, in which patterns of interaction or interdependency across the borders of the bounded region are ignored or distorted, and shape effects, in which the shape imposed on the bounded area affects the perceived interactions between phenomena.

boundary feature weight

One of two types of feature weights that allow control of how labels are placed relative to polygon features in ArcMap. Higher feature weights prevent labels from being placed over features. A high boundary feature weight keeps labels off of the edge of a polygon, but does not prevent the label from being placed within the boundary.

boundary line

A division between adjacent political entities, tracts of private land, or geographic zones. Boundary lines may be imaginary lines, physical features that follow those lines, or the graphical representation of those lines on a map. Boundary lines between privately owned land parcels are usually called property lines.

boundary monument

An object that marks an accurately surveyed position on or near a boundary.

boundary network

In Survey Analyst - Cadastral Editor, an irregular mesh of parcel boundaries, connection lines and control points representing a cadastral fabric. A boundary network represents parcels implicitly joined together, and is used by least-squares adjustment to distribute error from fixed control points based on the precision of boundary dimensions (bearings and distances).

boundary survey

A map that shows property lines and corner monuments of a parcel of land.

bounding rectangle

The rectangle, aligned with the coordinate axes and placed on a map display, that encompasses a geographic feature or group of features or an area of interest. It is defined by minimum and maximum coordinates in the x and y directions and is used to represent, in a general way, the location of a geographic area.

Bowditch rule

A widely used rule for adjusting a traverse that assumes the precision in angles or directions is equivalent to the precision in distances. This rule distributes the closure error over the whole traverse by changing the northings and eastings of each traverse point in proportion to the distance from the beginning of the traverse. More specifically, a correction factor is computed for each point as the sum of the distances along the traverse from the first point to the point in question, divided by the total length of the traverse. The correction factor at each point is multiplied by the overall closure error to get the amount of error correction distributed to the point's coordinates. The compass rule is also known as the Bowditch rule, named for the American mathematician and navigator Nathaniel Bowditch (1773-1838).


In ArcGIS Network Analyst, an object used in vehicle routing problem (VRP) analysis. A break can be used to model a specified period of rest along a route within a vehicle routing problem VRP instance.


A line in a TIN that represents a distinct interruption in the slope of a surface, such as a ridge, road, or stream. No triangle in a TIN may cross a breakline (in other words, breaklines are enforced as triangle edges). Z-values along a breakline can be constant or variable.

brightness theme

In 3D Analyst and Spatial Analyst for ArcView 3.x, a grid theme whose cell values are used to vary the brightness of another grid theme. The cell values in one grid can be visually plotted against those in another. Most commonly, hillshade grids are used as brightness themes for elevation grids. The effect is to display the elevation surface in relief.

browse graphic

An image associated with data to provide a general idea of what the service looks like. In ArcWeb Services, the browse graphic appears in the Content Library and Service Library and is defined in the metadata.


A tree data structure used for indexing data within a database or file system implementation. In a B-tree structure, data is sorted into a set of hierarchical nodes, usually using only three or four levels. The limited number of levels makes effective searches possible, because most of the nodes in the tree do not have to be accessed during a search.


A zone around a map feature measured in units of distance or time. A buffer is useful for proximity analysis.


In computing, a flaw or error in a software program or hardware component that prevents it from performing the way it should.


In ArcGIS, the process of creating a network system. For geometric networks, this includes establishing connectivity, creating network features, and creating logical network tables. For network datasets, this includes establishing connectivity, creating network elements, and assigning network attribute values.

build parcel

In Survey Analyst - Cadastral Editor, a cadastral fabric editing command that creates a parcel from construction lines and legal records.


A Web tool for creating and modifying content and publishing services. Users can access Builder through the ArcWeb Services Web site.


A set of conductors that provide communications links between the various functional components of a computer, such as memory and peripheral devices.

business table

In a geodatabase, the spatially-enabled DBMS table that holds the main attribute values of a dataset. A business table with a spatial column is a feature class, and a business table with a raster column is a raster dataset or a raster catalog. In the database, the business table name is the dataset name.


A discrepancy between existing coordinates and computed coordinates that occurs when the final point of a closed traverse has known coordinates and the final course of a traverse computes different coordinates for the same survey point.


A command that executes a function, macro, or custom code when clicked.


The smallest addressable unit of data storage within a computer, almost always equivalent to 8 bits and containing one character.