M
macro
A sequence of commands that can be executed as one command. Macros can be written to perform frequently used or complex operations. In ArcCatalog and ArcMap, you use VBA to create macros.
major axis
The longer axis of an ellipse or spheroid.
make permanent
When using Spatial Analyst, this option creates a permanent raster from a temporary result from analysis.
map
A graphical representation of geographic information. It includes geographic data and other elements such as a title, North arrow, legend, and scale bar. You can interactively display and query the geographic data on a map and prepare a printable map by arranging the map elements around the data in a visually pleasing manner.
The document used in ArcMap to display and work with geographic data. A map contains one or more layers of geographic data and various supporting map elements such as a scale bar. Layers on a map are contained in data frames.
Map Algebra
The analysis language for the Spatial Analyst. It provides access to a wide range of additional functions not included in the user interface, and enables you to build more complex expressions and process them as a single command.
map display
A graphic representation of a map on the computer screen.
map document
In ArcMap, the disk-based representation of a map. Map documents can be printed or embedded in other documents. Map documents have an .mxd file extension.
map element
A graphic component, such as a scale bar, North arrow, title, or legend, that helps describe the geographic data on the map.
map feature
See feature.
Map LIBRARIAN
A set of software tools to manage and access large geographic datasets in a map library. Map LIBRARIAN commands create and define a map library, move data in and out of a library, query the data in a map library, and display the results of a query.
map projection
See projection.
map scale
See scale.
map surround
See map element.
map template
In ArcMap, a kind of map document that provides a quick way to create a new map. Templates can contain data, a custom interface, and a predefined layout that arranges map elements, such as North arrows, scale bars, and logos, on the virtual page. Map templates have an .mxt file extension.
map tips
Displays on-screen descriptions of map features when you pause the mouse pointer over the feature.
map units
The units—for example, feet, miles, meters, or kilometers—in which the coordinates of spatial data are stored.
mathematical functions
Functions within the Raster Calculator of Spatial Analyst. They apply a mathematical function to the values of a single input grid. There are four groups of mathematical functions available: logarithmic, arithmetic, trigonometric, and powers.
mathematical operators
Operators within the Raster Calculator of the Spatial Analyst. They apply a mathematical operation to the values in two or more input grids. There are three groups of mathematical operators available: Arithmetic, Boolean, and Relational.
Arithmetic: *, /, -, +
Boolean: And, Or, Xor, Not
Relational: ==, >, <, <>, .=, <=
menu
A command that arranges other commands into a list.
menu item
An item in a list of commands displayed from a menu.
merge policy
In geodatabases, all attribute domains have a merge policy associated with them. When two features are merged into a single feature in the Editor, the merge policies dictate what happens to the value of the attribute to which the domain is associated. Standard merge policies are default value, sum, and weighted average.
meridian
The reference line on the earth's surface formed by the intersection of the surface with a plane passing through both poles. This line is identified by its longitude. Meridians run north-south between the poles.
metadata
Information about GIS data describing a collection of data. Metadata for geographical data may include the source of the data, its creation date and format, its projection, scale, resolution, and accuracy, and its reliability with regard to some standard. ArcCatalog stores metadata in XML (extensible markup language), so the same metadata can be viewed in many different ways using different style sheets.
Metadata consists of properties and documentation. Properties are derived from the data source, while documentation is entered by a person. By default, ArcCatalog automatically creates and updates metadata, which is stored as well-formed XML data in a file alongside the data or within a geodatabase. Metadata for a folder can also consist of a well-formed HTML file describing its contents.
metadata element
One piece of data within a data source's metadata. In the XML file, each element has an opening and closing tag. Elements can appear many times in an XML file; these are called repeating elements. For example, in a shapefile's metadata, an "<attr>" element might represent one of its attributes. Therefore, the "<attr>" element will appear many times—once for each attribute.
metadata profile
An extension to the FGDC's Content Standard for Digital Geospatial Metadata. Additional elements defined by ESRI are recorded in the ESRI Metadata Profile.
method
An action that an object is capable of performing. Objects that belong to the same class all have the same methods. For example, all form objects can execute a method called "Show and Hide".
Microsoft Access
A commercial RDBMS used for the personal geodatabase.
Microsoft SQL Server
A commercial RDBMS that is supported with ArcSDE.
minimum bounding rectangle
A rectangle, oriented to the x- and y-axes, that bounds a geographic feature or a geographic dataset. It is specified by two coordinate pairs: xmin, ymin and xmax, ymax. For example, the extent defines a minimum bounding rectangle for a coverage.
minor axis
The shorter axis of an ellipse or spheroid.
model
An abstraction of reality used to represent objects, processes, or events.
A set of clearly defined analytical procedures used to derive new information.
A data representation of reality (for example, vector data model, TIN data model, raster data model).
mouse mode
Also known as relative mode, mouse mode is one of the ways in which a digitizing tablet operates. In mouse mode, the digitizer puck behaves just like a mouse; there is no correlation between the position of the screen pointer and the surface of the digitizing tablet, but you can choose interface elements with the pointer. See also digitizing mode.
MSDE
Microsoft Database Engine. A client/server data engine based on Microsoft SQL Server. Can be used with ArcSDE for SQL Server.
multipart feature
A feature that is composed of more than one physical part but only references one set of attributes in the database. For example, in a layer of states, the State of Hawaii could be considered a multipart feature. Although composed of many islands, it would be recorded in the database as one feature.
multipoint feature
A feature that consists of more than one point but only references one set of attributes in the database. For example, a system of oil wells might be considered a multipoint feature, as there is a single set of attributes for multiple well holes.
multiuser database
A geodatabase in an RDBMS served to client applications (for example, ArcMap) by ArcSDE. Multiuser geodatabases can be very large and support multiple concurrent editors. Supported on a variety of commercial RDBMS including Oracle, Microsoft SQL Server, IBM DB2, and Informix.

L
label
Text on a map that provides map readers with additional information about a feature. ArcMap can label features on the fly with any of their attributes (or with text from several fields) and has advanced options for label placement and visibility. Labels can be made into annotation layers and then stored in geodatabases.
label point
A feature class in a coverage used to represent point features and identify polygons.
lag
The line (vector) that separates any two locations. A lag has length (distance) and direction (orientation).
LAN
Local area network. A computer data communications technology that connects computers at the same site-for example, all computers in the same building. Computers and terminals on a LAN can freely share data and peripheral devices such as printers and plotters. LANs are composed of cabling and special data communications hardware and software. See also WAN.
latitude
The angular distance (usually measured in degrees) north or south of the equator. Lines of latitude are also referred to as parallels. See also geocentric latitude and geodetic latitude.
latitude of center
The latitude value that defines the center (and sometimes origin) of a projection.
latitude of origin
The latitude value that defines the origin of the y-coordinate values for a projection.
latitude—longitude
A spherical reference system used to measure locations on the earth's surface. Latitude and longitude are angles measured from the earth's center to locations on the earth's surface. Latitude measures angles in a north-south direction. Longitude measures angles in an east–west direction.
layer
A collection of similar geographic features—such as rivers, lakes, counties, or cities—in a particular area or place referenced together for display on a map. A layer references geographic data stored in a data source, such as a coverage, and defines how to display it. You can create and manage layers as you would any other type of data in your database.
A feature class in a shared geodatabase managed with SDE 3.
layout
The design or arrangement of elements—such as geographic data, North arrows, legends, and scale bars—on a digital map display or printed map.
layout view
The view for laying out your map in ArcMap. Layout view shows the virtual page upon which you place and arrange geographic data and map elements—such as titles, legends, and scale bars—for printing. See also data view.
least-cost path
See shortest path.
left-right topology
The topological data structure ArcInfo uses to represent contiguity between polygons. Left-right topology supports analysis functions such as adjacency. See also topology.
legend
A list of symbols appearing on the map; includes a sample of each symbol and text describing which feature each symbol represents.
library
A collection of spatially related ArcStorm or Map LIBRARIAN layers. A library has a spatial extent that applies to all layers in the library.
linear dimension
A dimension whose length doesn't represent the true distance between the begin and end dimension points. Linear dimensions can be vertical, horizontal, or rotated. A vertical dimension's line represents the vertical distance between the begin and end dimension points. A horizontal linear dimension's line represents the horizontal distance between the begin and end dimension points. A rotated linear dimension is a dimension whose line is at some angle to the baseline and whose length represents the length of the dimension line itself, not the baseline.
linear feature
A geographic feature represented by a line or set of lines. A line connects two or more x,y coordinate pairs. Rivers, roads, and electric and telecommunication networks are all linear features.
linear units
The unit of measurement on a plane or a projected coordinate system, often meters or feet. Map projection parameters (such as the false easting and false northing) are defined in linear units.
line of sight
A graphic line between two points on a surface that shows whether or not the view along the line is obstructed.
local functions
This group of Spatial Analyst functions computes an output raster where the output value at each location is a function of the input value at the same location.
location query
Also called spatial query. Selection of features by their geometric relationship with other features. See also query.
logarithm functions
Functions within the Raster Calculator of Spatial Analyst. They perform exponential and logarithmic calculations on input grids and numbers.
There are six logarithmic functions: base e (Exp), base 10 (Exp10), and base 2 (Exp2) exponential capabilities, and natural (Log), base 10 (Log10), and base 2 (Log2) logarithmic capabilities.
logical network
An abstract representation of a network. A logical network consists of edge, junction, and turn elements and the connectivity between them. You can ask a logical network which elements are connected, but you cannot ask it for the geometry of these elements. A logical network does not contain any coordinate data, so you cannot ask it for the location of its elements. For this you need a geometric network. In a logical network, an edge element is connected to two junction elements (a from-junction and a to-junction), and a junction can have zero or more edges connected to it. A turn has a from-edge, a junction, and a to-edge. Each element can also have many weights associated with it. Weights are typically used to describe the cost to traverse an edge or turn or the cost to pass through a junction.
long transaction
An edit session on a feature dataset that may last from a few minutes to several months. Long transactions are managed by ArcSDE's versioning mechanism.
longitude
The angular distance (usually measured in degrees) east or west of a prime meridian.
longitude of center
The longitude value that defines the center (and sometimes origin) of a projection.
longitude of origin
The longitude value that defines the origin of the x-coordinate values for a projection.

K
key attributes
To join two tables together, each table must have a column containing the same values. For example, a country feature with a "Name" attribute can be joined to the appropriate record in a table of demographic data that has a "Country_Name" column. See also relate, relationship class, primary key, and foreign key.
Kriging
A geostatistical interpolation method based on statistical models that include autocorrelation (the statistical relationship among the measured points). Kriging weights the surrounding measured values to derive a prediction for an unmeasured location. Weights are based on the distance between the measured points, the prediction locations, and the overall spatial arrangement among the measured points.

J
job
A task scheduled on a Geoprocessing Server for immediate or future remote processing. A job can involve a single tool or a batch mode execution.
join
The process of attaching tabular data to geographic features. Attributes in an attribute table are appended to the features in a spatial data table using an attribute or item common to both tables. See also relational join.
junction element
A network feature that occurs at the intersection of two or more edges or at the endpoint of an edge that allows the transfer of flow between edges. See also logical network.

I
Identify
To click a feature with the identify tool, which opens a window showing that feature's attributes.
identity
The topological overlay of a coverage A (input) with a polygon coverage B (identity) that computes the geometric intersection of the two coverages. The output coverage preserves all the features of A plus those portions of B which overlap A. Features from coverage A are preserved in the output dataset and receive attributes from the polygons in B which they intersect. For example, a road (input coverage, arc feature class) passing through two counties (identity coverage) would be split into two arc features, each with the attributes of the road and the county it passes through. See also intersect and union. See also intersect and union.
image
A raster-based representation or description of a scene, typically produced by an optical or electronic device. Common examples include remotely sensed data (for example, satellite data), scanned data, and photographs. An image is stored as a raster dataset of binary or integer values that represent the intensity of reflected light, heat, or other range of values on the electromagnetic spectrum. An image may contain one or more bands. See also raster and band.
indeterminate flow direction
For an edge feature, occurs when the flow direction cannot be determined from the topology of the network, the locations of sources and sinks, and the enabled or disabled states of features.
index
A special data structure used in a database to speed searching for records in tables or spatial features in geographic datasets. ArcInfo supports both spatial and attribute indexes.
INFO database
The contents of a set of INFO data files, feature attribute tables, and related files stored in an ArcInfo workspace under a subdirectory named INFO. This subdirectory contains all feature attribute tables for the coverages in the workspace.
Informix
A commercial RDBMS supported by ArcSDE.
instance
The name of the process running on the ArcSDE server that allows connections and access to spatial data. Also called Service.
integrated feature dataset
Topologically associated feature classes in a geodatabase are stored in an integrated feature dataset. You can use the topological editing tools in ArcMap to maintain the topological associations of features in an integrated feature dataset.
interpolate
To predict values for a surface from a limited number of sample data points.
interpolation
A set of Spatial Analyst functions that predict values for a surface from a limited number of sample data points, creating a continuous raster.
intersect
The topological integration of two spatial datasets that preserves features that fall within the area common to both input datasets. Compare with identity and union.
Inverse Distance Weighted (IDW)
An interpolation method in which cell values are estimated by averaging the values of sample data points in the vicinity of each cell. The closer a point is to the center of the cell being estimated, the more influence, or weight, it has in the averaging process.
IP address
The server's address on the network. The address consists of four numbers, each separated by a ".".
ISO
International Standards Organization. A worldwide federation of national standards bodies (for example, ANSI from the United States). ISO maintains many computing standards, including a SQL standard.
item
A column of information in an INFO table.
An element in the Catalog tree in ArcCatalog. The Catalog tree can contain both geographic data sources and nongeographic elements such as folders, folder connections, and file types.

H
Help Node
A branch in the ArcToolbox tree providing overview Help for ArcToolbox toolsets.
hillshade
The hypothetical illumination of a surface. A hillshade raster can be calculated for a given surface, or hillshading can be applied on the fly to surfaces and areal features in a scene.
histogram
A Spatial Analyst function that creates a histogram from the values in a raster dataset. By default, the value field is represented on the x-axis and the number of cells with this value (count) is represented on the y-axis. You can control the field that is displayed in the histogram by setting the field in the Symbology tab of the Layer Properties dialog box.
HTML
Hypertext markup language. An HTML file contains text and tags instructing an Internet browser application how to present the text. For example, <B>24</B> will display the text "24" in bold.
hyperlink
Displays linked data, such as an image or Web page, when you click on it.

G
Gauss-Krüger
A projected coordinate system used in Europe that divides the area into zones six degrees wide. Very similar to the UTM coordinate system.
geocentric latitude
Defined as the angle between the equatorial plane and a line from a point on the surface to the center of the sphere or spheroid.
geocoding
The process of creating geometric representations for locations (such as point features) from descriptions of locations (such as addresses).
geocoding index
An index on geocoding reference data used by geocoding services.
geocoding reference data
Data that a geocoding service uses to determine the geometric representations for locations.
geocoding service
An object that defines a process for creating geometric representations for locations (such as point features) from descriptions of locations (such as addresses).
geodatabase
An object-oriented geographic database that provides services for managing geographic data. These services include validation rules, relationships, and topological associations. A geodatabase contains feature datasets and is hosted inside of a relational database management system.
geodatabase data model
Geographic data model that represents geographic features as objects in an object-relational database. Features are stored as rows in a table; geometry is stored in a shape field. Supports sophisticated modeling of real-world features. Objects may have custom behavior.
geodesic
The shortest distance between two points on the surface of a spheroid. Any two points along a meridian form a geodesic. See also great circle.
geodetic latitude
Defined as the angle formed by the perpendicular to the surface at a point and the equatorial plane. On a spheroid, the perpendicular doesn't intersect the center of the spheroid in the equatorial plane.
geographic coordinate system
A reference system using latitude and longitude to define the locations of points on the surface of a sphere or spheroid. See also projected coordinate system.
geographic coordinates
A measurement of a location on the earth's surface expressed in degrees of latitude and longitude. See also projected coordinates.
geographic data
The locations and descriptions of geographic features. The composite of spatial data and descriptive data.
geographic database
A collection of spatial data and related descriptive data organized for efficient storage and retrieval by many users.
geographic transformation
A method that converts data between two geographic coordinate systems (datums). Also known as a datum transformation.
geolocation
The process of creating features from tabular data by matching the tabular data to a spatial location. Examples of geolocation is creating point features from a table of x,y coordinates, addresses, and linear events. Points can be created by matching addresses to streets.
geometric network
Represents a one-dimensional linear network such as a road system, a utility network, or a hydrologic network. Geometric networks contain feature classes that play a topological role in the network. These feature classes are homogeneous collections of one of these four network feature types: simple junction feature, complex junction feature, simple edge feature, and complex edge feature. More than one feature class can have the same type of network feature.
geoprocessing
GIS operations such as geographic feature overlay, coverage selection and analysis, topology processing, and data conversion.
Geoprocessing Server
A UNIX or Windows NT computer that handles geoprocessing tasks remotely. It includes a utility to schedule remote processing.
georeference
The process of defining how raster data is situated in map coordinates. Georeferencing raster data allows it to be viewed, queried, and analyzed with other geographic data.
georelational data model
A geographic data model that represents geographic features as an interrelated set of spatial and descriptive data. The georelational model is the fundamental data model used in coverages—for example, it pulls together geometry and attributes that are stored in different places.
Geospatial Data Clearinghouse
Sponsored by the FGDC. A decentralized system of servers on the Internet that contain metadata describing available geographic data. This metadata follows the format specified by the Content Standard for Digital Geospatial Metadata to facilitate querying and enforce a consistent presentation across all servers.
GIS
Geographic information system. An organized collection of computer hardware, software, geographic data, and personnel designed to efficiently capture, store, update, manipulate, analyze, and display all forms of geographically referenced information.
A GIS may be used for a project (also called project GIS, or single-user GIS), by a department of an organization to support a key function of that department (called departmental GIS), or by an organization to support daily activities and strategic decision making (called enterprise GIS).
global functions
This group of Spatial Analyst functions computes an output raster where the output value at each location is potentially a function of all the cells in the input raster.
graticule
A graphic representation on a map of the network of parallels and meridians (latitude and longitude) that subdivide the earth's surface.
great circle
Any circle on the surface of a sphere formed by the intersection of the surface with a plane passing through the center of the sphere. The shortest path between any two points lies on a great circle and is therefore important to navigation. All meridians and the equator are great circles on the earth defined as a sphere (Snyder and Voxland, 1989). See also geodesic.
Greenwich prime meridian
The prime meridian located in Greenwich, England. A prime meridian defines the origin of longitude values.
grid
A geographic representation of the world as an array of equally sized square cells arranged in rows and columns. Each grid cell is referenced by its geographic x,y location. See raster.
grid cell
See raster cell.
ground control point
A location of known x,y coordinates used to georeference a raster. A ground control point links a location on a raster to a location in map coordinates.
group layer
Several layers that appear and act like a single layer in the table of contents in ArcMap.

F
face
Triangles form the faces on a TIN surface. Each face on a TIN surface is defined by three edges and three nodes, and is adjacent to one to three faces on the surface. TIN faces store aspect and slope information and may have tag values.
false easting
A linear value added to the x-values, usually to ensure that all map coordinates are positive. See also false northing.
false northing
A linear value added to the y-values, usually to ensure that all map coordinates are positive. See also false easting.
feature
An object class in a geodatabase that has a field of type geometry. Features are stored in feature classes.
A representation of a real-world object.
A point, line, or polygon in a coverage, shapefile, or geodatabase feature class.
feature attribute table
A table used to store attribute information for a specific coverage feature class. ArcInfo maintains the first several items of these tables. Feature attribute tables supported for coverages include the following:
<cover>.PAT for polygons or points
<cover>.AAT for arcs
<cover>.NAT for nodes
<cover>.RAT for routes
<cover>.SEC for sections
<cover>.PAT for regions
<cover>.TAT for annotation (text) where <cover> is the coverage name.
feature class
The conceptual representation of a geographic feature. When referring to geographic features, feature classes include point, line, area, and annotation. In a geodatabase, an object class that stores features and has a field of type geometry.
A classification describing the format of geographic features and supporting data in a coverage. Coverage feature classes for representing geographic features include point, arc, node, route-system, route, section, polygon, and region. One or more coverage features are used to model geographic features; for example, arcs and nodes can be used to model linear features such as street centerlines. The tic, annotation, link, and boundary feature classes provide supporting data for coverage data management and viewing.
The collection of all the point, line, or polygon features or annotation in a CAD dataset.
feature dataset
In geodatabases, a collection of feature classes that share the same spatial reference. Because the feature classes share the same spatial reference, they can participate in topological relationships with each other such as in a geometric network. Several feature classes with the same geometry may be stored in the same feature dataset. Object classes and relationship classes can also be stored in a feature dataset.
FGDC
Federal Geographic Data Committee. An interagency committee, organized in 1990, that promotes the coordinated use, sharing, and dissemination of geospatial data on a national basis. The FGDC is composed of representatives from 16 Cabinet-level and independent U.S. federal agencies. The FGDC authored the Content Standard for Digital Geospatial Metadata.
field
A column in a table. Each field contains the values for a single attribute.
file
A set of related information that a computer can access by a unique name (for example, a text file, a data file, a DLG file). Files are the logical units managed on disk by the computer's operating system. Files may be stored on tapes or disks.
file type
Files that are not geographic data sources can appear in ArcCatalog if they have been added to the file types list. A file type consists of a description of the file's format (such as "Text Document"), the file extension associated with this type of file (such as ".txt"), and the icon used to represent these files.
flag
In ArcMap, an object that is placed on a network to specify the starting point for a trace task.
flattening
A measure of how much a spheroid differs from a sphere. The flattening is the ratio of the semimajor axis minus the semiminor axis to the semimajor axis. Known as "f" and often expressed as a ratio. Example: 1/298.3. Also known as the ellipticity.
flow direction
The direction in which commodities flow through edge elements in a network.
focal functions
This group of Spatial Analyst functions computes an output raster where the output value at each location is a function of the input cells in some specified neighborhood of the location.
folder
A location on a disk containing a set of files and other folders. See also directory.
folder connection
A top-level branch of the Catalog tree in ArcCatalog that provides quick access to a location in the file system. You can make connections to hard drives, folders, and geodatabases.
foreign key
A column or combination of columns in one table whose values match the primary key in another table. A value in the foreign key can only exist if there is a corresponding value in the primary key (unless the value is NULL). Foreign key–Primary key relationships define a relational join.
Used to create a relationship class, the foreign key resides in the destination object class. To join two object classes together, the primary key and foreign key must share the same values.
See also primary key, relate, and relationship class.
format
The pattern into which data is systematically arranged for use on a computer. A file format is the specific design of how information is organized in the file. For example, ArcInfo has specific, proprietary formats used to store coverages. DLG, DEM, and TIGER are geographic datasets with different file formats.
freeze
When exploring a table's contents, you can fix a column in place at the left side of the table. When you scroll horizontally through the table's columns, the frozen column stays in place while the other columns scroll normally. For example, freeze the "Country_name" column so it's easy to see which country has which population or birth rate.
function
See spatial function.
fuzzy tolerance
An extremely small distance used to resolve inexact intersection locations due to the limited arithmetic precision of computers. It defines the resolution of a coverage resulting from the Clean operation or a topological overlay operation such as Union, Intersect, or Clip.

E
eccentricity
A measurement of how much an ellipse deviates from a true circle. Measured as the square root of the quantity [(1-b2/a2)1/2], or 1.0 minus the square of the ratio of the semiminor axis to the semimajor axis. The square of the eccentricity, "e2", is commonly used with the semimajor axis, "a", to define a spheroid in map projection equations.
edge
The linear segments between nodes in a TIN surface. Edges store information about the faces that they border. Linear features and the perimeters of polygon features used to generate a TIN become edges in the TIN.
edge element
A network feature that has a length through which commodity flows. See also logical network.
edge–edge rule
In geodatabases, a connectivity rule that establishes that an edge of type A may connect to an edge of type B through a junction of type C. Edge–edge rules always involve a junction type.
edge–junction cardinality
A rule may exist that allows an edge of type A to connect to a junction of type B. By default, any number of edges of type A can connect to a single junction of type B. You may want to restrict this. You can specify that between two and five edges of type A can connect to a junction of type B, but if there are less than two edges, or more than five edges, the connectivity rule is being violated. Similarly, you can restrict the number of junctions of type C that can connect to any junction of type D. This range of permissible connections is edge–junction cardinality.
edge–junction rule
A connectivity rule in geodatabases establishing that an edge of type A may connect to a junction of type B.
edit box
A command that displays text typed by a person or derived from another source. For example, in ArcMap you can type the scale at which you want to see the map. Also known as a text box.
edit cache
A setting used in spatial data editing in ArcMap that causes the features visible in the current map extent to be held in memory on your local machine. Designed to be used when working with large amounts of data, an edit cache results in faster editing because ArcMap doesn't have to retrieve the data from the server.
edit session
In ArcMap, all editing takes place within an edit session. An edit session begins when you choose Start Editing from the Editor menu and ends when you choose Stop Editing.
Editor toolbar
A set of tools that allows you to create and modify features and their attributes in ArcMap.
element
See map element.
ellipse
A geometric shape equivalent to a circle that is viewed obliquely; a flattened circle.
ellipsoid
When used to represent the earth, the three-dimensional shape obtained by rotating an ellipse about its minor axis. This is an oblate ellipsoid of revolution, also called a spheroid.
ellipticity
The degree to which an ellipse deviates from a true circle. The degree of flattening of an ellipse, measured as 1.0 minus the ratio of the semiminor axis to the semimajor axis.
enabled feature
In geodatabases, a network feature that allows flow to pass through it.
enclosures
Files describing the contents of a data source can be enclosed in the metadata. A copy of the file is contained within the metadata. Enclosing files in metadata works the same way as enclosing files in an e-mail message.
equal area projection
A projection on which the areas of all regions are shown in proportion to their true areas. Shapes may be greatly distorted (Snyder and Voxland, 1989). See also conformal projection.
equator
The parallel of reference that defines the origin of latitude values, 0 degrees north or south.
equatorial aspect
A planar projection with its central point located at the equator.
equivalent projection
A projection that maintains scale along one or more lines, or from one or two points to all other points on the map. Also called equidistant projection. See also conformal projection.
erase
An ArcInfo command that erases the input coverage features that overlap the erase coverage polygons.
Euclidean distance
See straight line distance.
event
Objects execute code in response to an event. Events occur when the user interacts with an application. For example, clicking a button closes a form. The event triggered by clicking the button is the form closing.
executable (EXE)
A program file created from one or more source code files translated into machine code and linked together.
exit state
The condition of a tool upon closure. If a tool fails due to a programming bug or command failure, the exit state will be "failed".
extent
The coordinate pairs defining the minimum bounding rectangle (xmin, ymin and xmax, ymax) of a data source. All coordinates for the data source fall within this boundary.
extent rectangle
A rectangle that is displayed in one data frame, showing the size and position of another data frame.
Extract wizard
An ArcToolbox wizard that selects features from a coverage based on attribute values to create a new coverage.
extrusion
You can extrude 2D point, line, and area features in a scene into lines, planes, and solids. Use extrusion to show the depth of well point features or the height of building footprint polygons.

D
dangle tolerance
The minimum length allowed for dangling arcs in coverages in ArcInfo's Clean process. Clean removes dangling arcs that are shorter than the dangle tolerance. Also known as the dangle length.
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 (undershoot), where arcs don't connect properly, or where an arc was digitized past its intersection with another arc (overshoot). A dangling arc is not always an error. For example, dangling arcs can represent cul-de-sacs in street centerline maps.
data
A collection of related facts usually arranged in a particular format and gathered for a particular purpose.
data dictionary
A set of tables containing information about data. ArcSDE and the geodatabase have data dictionary tables containing information about the GIS data in the database.
data frame
In ArcMap, a frame on the map that displays layers occupying the same geographic area. You may have one or more data frames on your map depending on how you want to organize your data. For instance, one data frame might highlight a study area and another might provide an overview of where the study area is located.
data integrity
Refers to the accuracy and consistency of data in a database. Data integrity is maintained through the creation of attribute domains and through mandatory conflict resolution between versions of a dataset.
data model
See georelational data model and geodatabase data model.
data source
Geographic data (coverage, shapefile, raster, or feature class) in a geodatabase.
data type
The attribute of a variable or field (column) that determines the kind of data it can store. Common data types are character, integer, decimal, single, double, and string.
data view
An all-purpose view in ArcMap for exploring, displaying, and querying geographic data. This view hides all map elements such as titles, North arrows, and scale bars. See also layout view.
database
A collection of related data organized for efficient retrieval of information.
A logical collection of interrelated information managed and stored as a unit, usually on some form of mass storage system such as magnetic tape or disk. A GIS database includes data about the spatial location and shape of geographic features recorded as points, lines, areas, pixels, grid cells, or TINs, as well as their attributes.
database administrator
One who manages a database—sets up users, security, backup, and recovery procedures for all data and optimizes physical data storage for best performance.
database connection
A connection in ArcCatalog to a database. Database connections have a state—they are either connected to or disconnected from the database. If you delete a database connection, you only delete the connection itself, not the database or its contents. In general, when you create a database connection, you choose a data provider that will retrieve your data from the appropriate database. To work with the features in a multiuser geodatabase, use ArcSDE as the data provider. OLE DB providers let you access data in many different databases.
database management system
See DBMS.
dataset
Any feature class, table, or collection of feature classes or tables in the geodatabase.
A named collection of logically related data items arranged in a prescribed manner.
datum
A set of parameters and control points used to accurately define the three-dimensional shape of the earth. The datum defines part of a geographic coordinate system that is the basis for a planar coordinate system. For example, the North American Datum for 1983 (NAD83) is the datum for map projections and coordinates within the United States and throughout North America.
datum transformation
See geographic transformation.
DBMS
Database management system. A set of computer programs for organizing the information in a database. A DBMS supports the structuring of the database in a standard format and provides tools for data input, verification, and storage.
decimal degrees
Degrees of latitude and longitude expressed in decimal format rather than in degrees, minutes, and seconds.
default junction type
In geometric networks, two edge types may be connectable through more than one junction type. You can establish which of those junction types is the default for connecting the two edge types. This junction type is the default junction type. An edge may also have a default end junction type. This is the junction that is used for the free ends of new edges.
degree slope
One of the ways slope is measured (measured from 0&#821190; degrees).
DEM
Digital elevation model.
A digital representation of a continuous variable over a two-dimensional surface by a regular array of z-values referenced to a common datum. Digital elevation models are typically used to represent terrain relief. Also referred to as digital terrain model (DTM).
An elevation database for elevation data by map sheet from the National Mapping Division of the U.S. Geological Survey (USGS).
The format of the USGS digital elevation datasets.
density
A Spatial Analyst function that distributes the quantity or magnitude of point or line observations over a unit of area to create a continuous raster— for example, population per square kilometer.
destination
The secondary object in a relationship. For example, a table containing attributes that are associated with features in a feature class. See also relationship and origin.
The destination point for a path when performing the Shortest Path function with Spatial Analyst.
determinate flow direction
For an edge feature, occurs when the flow direction can be determined from the topology of the network, the locations of sources and sinks, and the enabled or disabled states of features.
digitizing
To encode geographic features in digital form as x,y coordinates.
The process of converting the features on a paper map into digital format. When you digitize a map, you use a digitizing tablet, or digitizer, which is connected to your computer. You then trace over features with a digitizer puck, which is similar to a mouse. The x,y coordinates of these features are automatically recorded and stored as spatial data.
Heads-up digitizing features from on-screen data (rasters, for example).
digitizing mode
Also called absolute mode, digitizing mode is one of the ways in which a digitizing tablet operates. In digitizing mode, the location of the tablet is mapped to a specific location on the screen. Moving the digitizer puck on the tablet surface causes the screen pointer to move to precisely the same position. See also mouse mode.
dimension construction methods
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
A special kind of map 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 features are stored in a dimension feature class.
dimension feature class
In the geodatabase, dimension features are stored in a dimension feature class. Like other feature classes in the geodatabase, all features in a dimension feature class have a geographic location and attributes and can either be inside or outside of a feature dataset.
dimension style
A dimension feature's style describes its symbology, what parts of it are drawn, and how it is drawn. Every time you create a new dimension feature, it is assigned a particular style. A collection of dimension styles is associated with a dimension feature class.
dimensioning toolbar
A toolbar in ArcMap that facilitates the creation of dimension features.
direct connect
A two-tiered architecture for connecting to a spatial database. Direct connect does not require the ArcSDE application server to connect to a spatial database.
directory
A computer term identifying a location on a disk containing a set of files and other directories (subdirectories). Operating systems use directories to organize data. The location of a directory is specified with a path. Also called folder. See also folder.
disabled feature
A network feature through which flow is impossible.
discrete raster
A rater that typically represents phenomena that have clear boundaries and attributes that are descriptions or categories. Each cell in a discrete raster stores an integer value that represents a feature. In a grid of land cover, for example, the value 1 might represent forested land, the value 2 urban land, and so on. See also categorical raster.
disk
A storage medium consisting of a spinning disk coated with a magnetic material for recording digital information.
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 units
The units—for example, feet, miles, meters, or kilometers—ArcMap uses to report measurements, dimensions of shapes, and distance tolerances and offsets.
DLL
See dynamic link library.
documentation
Text in an item's metadata describing where the data came from, attribute definitions, and so on. Unlike properties, which are automatically derived from the data source, documentation must be manually entered using the metadata editor in ArcCatalog.
domain
See attribute domain and spatial domain.
double precision
Refers to a high level of coordinate accuracy based on the possible number of significant digits that can be stored for each coordinate. ArcInfo datasets can be stored in either single or double precision. Double-precision coverages store up to 15 significant digits per coordinate (typically 13 to 14 significant digits), retaining the accuracy of much less than one meter at a global extent. See also single precision.
drape
To set the base height for features of a surface using a surface. When you drape a layer over a raster surface, the resolution of the base surface is automatically downsampled to increase performance. You can change the resolution of the base surface if the default is unsatisfactory.
drawing priority
The order in which layers that occupy the same x,y,z positions are drawn in a scene. For example, if you have a road feature layer and an orthophoto draped over the same terrain model, the roads and raster may appear patchy or broken-up where they coincide. You can reduce the drawing priority for the raster so it will appear below the features. You can only change the drawing priority for areal features and surfaces.
dynamic link library (DLL)
Modules containing a set of routines that are called from procedures. A DLL is loaded and linked to your application at runtime by its calling modules (EXE or DLL).