- C / C++
- A high level programming language.
- CAD/CAM
- Computer-Aided Design/Computer Aided Manufacturing. Several CAD/CAM systems also include major features for GIS and automated mapping.
- CAD drawing
- The digital equivalent of a drawing, figure or schematic created using a CAD system. For example, a drawing file or DWG file in AutoCAD.
- cadastral parcel
- The smallest legally defined piece of land. Used for recording ownership and related attributes.
- cadastral survey
- A boundary survey taken for the purpose of taxation.
- cadastre
- A survey that creates, defines, retraces, or re-establishes the boundaries and subdivisions of public lands and private estates. The ownership, characteristics, and value of private lands are recorded for taxation purposes.
- calibration
- The process of choosing attribute values and computational parameters so that a model properly represents the real-world situation being analyzed. For example, in pathfinding and allocation, calibration generally refers to assigning or calculating appropriate values to be entered in impedance and demand items.
- capacity
- The maximum resource that can be assigned (allocated) to or be serviced by a center. For example, the capacity of a school is the number of students that can be enrolled there.
- Cartesian coordinate system
- A two-dimensional, planar coordinate system in which x measures horizontal distance and y measures vertical distance. Each point on the plane is defined by an x,y coordinate. Relative measures of distance, area, and direction are constant throughout the Cartesian coordinate plane.
- cartographic modeling
- The use of basic GIS manipulation functions or tools in a logical sequence to solve spatial problems.
- cartography
- The science of map making, including the art and technology of map-making.
- cartridge disk
- A type of magnetic memory disk enclosed in a plastic cartridge.
- CASE
- Computer-Aided Software Engineering. CASE tools are defined
programming rules for applying engineering principles, methods, techniques, and
concepts. These tools assist in accomplishing a definable engineering task in
the software design process by automating manual activities through structured
prototyping. This technique reduces customized development time, supplying
consistent code sets and supporting the entire software life cycle process.
- cathode ray tube (CRT)
- An electronic screen for displaying information or graphics. Also called a visual display device (VDU).
- CCITT
- Comité Consultatif Internationale de
Télégraphique et Téléphonique (Consultative
Committee on International Telephone and Telegraph). CCITT is a technical
committee of the International Telecommunications Union, a United Nations
organization in Geneva. It sets international communications recommendations
concerning standardization of data interfaces, modems, and data networks.
ArcInfo is fully compliant with CCITT Group IV, the Standard for raster data
compression. ArcInfo supports the following TIFF compression
schemes: CCITT Group 4 for black-and-white data (read only); CCITT Group 3,
one-dimensional encoding for black-and-white data; and PackBits.
- CD-ROM
- Compact Disk-Read Only Memory. CD-ROM is an optical media. A
CD-ROM 5.25-inch disk can hold about 650 megabytes of information. The ISO
9660 standard defines the format of data held on CD-ROM.
- cell
- See grid cell.
- census block
- The smallest unit used by the U.S. Census Bureau for reporting census data and for generating geographic base files such as DIME and TIGER® files. A block is enclosed by any natural or human-made features that form a logical boundary, such as roads, political boundaries, or shorelines. .
- center
- A discrete location that has a supply of a resource or commodity. In spatial interaction, a center is consider to have attractiveness.
- central processing unit (CPU)
- The part of the computer that controls the whole system..
- centroid (CPU)
- The mathematical or geographical center point of a polygon or the midpoint of a line. It is described as an x, y coordinate..
- CGM
- Computer Graphics Metafile is a graphic image exchange standard,
ANSI: x3.122-1986, ISO: 8632-1986, for graphic output file format. ArcInfo,
ArcView Version 2, and PC ARC/INFO support CGM.
- chain (CPU)
- A sequence of coordinates defining a complex line or boundary. See Arc, and String. .
- change detection
- Is the comparison of two images acquired at different times of the same area. Differences found between these two images can provide information concerning what alterations have occurred over time.
- character
- 1. A letter (e.g., a, b, c, or d), digit (e.g., 1, 2, or 3), or special graphic symbol (e.g., *, |, or -) treated as a single unit of data.
2. A data type for an attribute designating that values for the attribute will be represented using characters. For example, the character data type would be appropriate for the attribute COUNTRY, if the values assigned are like United States, Brazil, Canada, Thailand, and so on.
- checkin
- Checkin is the act of returning ArcStorm data which was previously checked out for update purposes. When modified data is checked in, all locks on the data are released.
- checkout
- Checkout is the act of taking selected data out of an ArcStorm database into a local coverage for editing purposes. When data is checked out, it is locked to prevent updates from other users. ArcStorm data cannot be modified directly, it must first be checked out.
- client/server
- A software system is said to have a client/server architecture when there is a central process (server) which accepts requests from multiple user processes (clients). ArcStorm is one example of a client/server architecture within ArcInfo.
- clip
- The spatial extraction of those features from one coverage that reside entirely within a boundary defined by features in another coverage (called the clip coverage)-clipping works much like a cookie cutter.
- choropleth map
- A map with areas colored or shaded such that the darkness or lightness of an area symbol is proportional to the density of the mapped phenomena or is symbolic of the class.
- classification
- Process of assigning individual observations of features into groups, categories, or classes.
- clearinghouse
- A place that stores and disseminates data.
- clip
- The process of extracting a portion of a coverage or map from a larger coverage, much like a cookie cutter.
- code
- A set of specific symbols and rules for representing data and programs so that they can be understood by the computer. See ASCII, FORTRAN, PASCAL, etc.
- COGO
- 1. Abbreviation of the term COordinate GeOmetry. Land surveyors use COGO functions to enter survey data, to calculate precise locations and boundaries, to define curves, and so on.
2. The name of the ArcInfo coordinate geometry software product.
- coincidence analysis
- Process of examining the co-occurrence of mapped phenomena.
- column
- The vertical dimension of a table. A column has a name and a data type applied to all values in the column.
- command
- A specific instruction to a computer program, issued by the user to perform a desired action.
- command line interface
- A software product that allows the user to type in commands at a prompt. Contrast to forms interface.
- commit
- To make permanent any changes made during a database transaction. Compare with roll back.
- composite map
- A single map created by joining together several separately digitized maps..
- computer aided drawing (CAD)
- Software with the capability of performing standard engineering drawing and architecture design functions. It is graphically oriented rather than geographically based. Unlike a GIS, the database is generally not structured to allow spatial analysis. However, some data developed in CAD systems can be incorporated into a GIS. .
- computer aided mapping (CAD)
- Software with the capability of performing standard mapping functions, typically mapping (CAM) using a vector format. Unlike a GIS, it cannot analyze or process the database. .
- concurrency management
- A database management process for maintaining consistency of the data while supporting simultaneous access by more than one user. A typical technique is to allow any number of users read access but to allow only one user to have write access. A second user wanting write access will have to wait until the first person completes their transaction.
- conditional operator
- A symbol or keyword specifying how to compare values. Conditional operators are used to query a database. Examples from SQL include:
= (equal to) BETWEEN
< (LESS THAN) LIKE
> (greater than) CONTAINING
- conflation
- A set of functions and procedures that aligns the arcs of one coverage with those of another and then transfers the attributes of one to the other. Alignment precedes the transfer of attributes and is most commonly performed by rubber-sheeting operations.
- connectivity
- The topological identification of connected arcs by recording the from- and to-node for each arc. Arcs that share a common node are connected. See also arc-node topology.
- constraints
- Limits imposed on a model. For example, in an interaction model, specifying that the number of trips generated from an origin to all destinations cannot exceed the origin's production capacity.
- contiguity
- The topological identification of adjacent polygons by recording the left and right polygons of each arc. See also polygon-arc topology.
- continuous data
- A surface for which each location has a specified or derivable value. Typically represented by a tin or lattice (e.g., surface elevation).
- contour
- A line connecting points of equal surface value.
- contour interval
- The difference in surface values between contours.
- coordinate
- A set of numbers that designate location in a given reference system, such as x,y in a planar coordinate system or an x,y,z in a three-dimensional coordinate system. Coordinates represent locations on the Earth's surface relative to other locations. See also vector and Cartesian coordinate system.
- coordinate geometry
- See COGO.
- coordinate system
- A reference system used to measure horizontal and vertical distances on a planimetric map. A coordinate system is usually defined by a map projection, a spheroid of reference, a datum, one or more standard parallels, a central meridian, and possible shifts in the x- and y-directions to locate x,y positions of point, line, and area features. In ArcInfo, a system with units and characteristics defined by a map projection. A common coordinate system is used to spatially register geographic data for the same area.
- corridor analysis
- A type of proximity analysis that utilizes specified distances or buffers along a line (e.g., amount of timber within 50 feet of a proposed power transmission line). See buffer.
- cost benefit analysis
- A comparison of the costs and benefits of the current system of processes versus a proposed GIS. A cost-benefit analysis is developed to assist with making an acquisition decision.
- Cover#
- A unique sequence number automatically generated by ArcInfo for each coverage feature. This internal number is used to directly access features and to describe topological relationships between coverage features. It is often referred to as the 'record number'.
- Cover-ID
- An integer identifier, assigned by the user, to relate geographic features and corresponding attribute data. Cover-ID is an item found in feature attribute tables, with 'Cover' replaced by the coverage name (e.g., for a soils coverage, the Cover-ID would be SOILS-ID). Feature-ID and User-ID are synonymous terms to Cover-ID.
- coverage
- 1. A digital version of a map forming the basic unit of vector data storage in ArcInfo. A coverage stores geographic features as primary features (such as arcs, nodes, polygons, and label points) and secondary features (such as tics, map extent, links, and annotation). Associated feature attribute tables describe and store attributes of the geographic features.
2. A set of thematically associated data considered as a unit. A coverage usually represents a single theme such as soils, streams, roads, or land use.
- coverage extent
- The coordinates defining the minimum bounding rectangle (i.e., xmin,ymin and xmax,ymax) of a coverage or grid. All coordinates for the coverage or grid fall within this boundary. In ARCPLOT and ARCEDIT, map extent is often set from the coverage extent. See also BND.
- coverage units
- The units (e.g., feet, meters, inches) of the coordinate system in which a coverage is stored.
- cross tabulation
- Comparison of attribute data by location in two or more map layers. Results are given in a tabular report format.
- cross-tile indexing
- A method used to index features that cross tile boundaries. Features that cross tile boundaries are stored as one or more features in each tile instead of as a single feature.
- CSSM
- The Content Standards for Spatial Metadata. A document produced
by the Federal Geographic Data Committee (FGDC) that describes spatial
metadata.
- cursor
- 1. A graphic pointer used with a mouse to point to a location on a terminal screen.
2. An internal pointer to a record in a table which provides a mechanism for processing a selected set of records. The cursor is moved one by one through the set while operations such as display, query and update are performed.
- cycle
- 1. In pathfinding, a cycle is a path or tour beginning and ending at the same node.
2. In tracing, a cycle is a set of arcs forming a closed polygon. Upstream and downstream directionality are undefinable in a cycle.
- DAL
- Data Access Language. Apple's former standard to allow
applications to communicate with relational databases. DAL is middleware on a
network. It is a program installed on the database server to provide a common
SQL access for all database servers on a network. Apple has licensed this
technology to Independence Technologies, Inc.
- dangle length
- Minimum length allowed for dangling arcs during the CLEAN process. CLEAN removes dangling arcs that are shorter than 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 identifies where a polygon does not close properly (e.g., undershoot), where arcs don't connect properly, or where an arc was digitized past its intersection with another arc (i.e., overshoot). A dangling arc is not always an error. For example, dangling arcs can represent cul-de-sacs in street centerline maps. See also dangling node.
- dangling node
- The endpoint of a dangling arc not connected to another arc.
- data (singular datum)
- Facts about real-world entities, organized for analysis. Includes results of observations or measurements of such entities. Three components of a datum are of direct relevance to GIS: (1) attribute information that describes the substance, characteristics, variables, values, and similar qualities of the entity; (2) geographical information that describes the position of the entity in space relative to other things in space; and (3) temporal information that describes the instant or period of time during which the entity is at a defined location or in an observed state or condition (attribute).
- data access security
- Measures taken to control system users' ability to view or modify data. These measures can include logical views of data and explicit access rights by group or individual users. See also access rights.
- database
- One or more structured sets of persistent data, managed and stored as a unit and generally associated with software to update and query the data. A simple database might be a single file with many records, each of which references the same set of fields. Examples of popular databases include dBase®, Oracle®, and SQLServer®. A GIS database includes data about the spatial locations and shapes of geographic features recorded as points, lines, areas, pixels, grid cells, or TINs, as well as the attributes.
- database design
- The formal process of analyzing facts about the real world into a structured database model. Database design is characterized by the following phases: requirement analysis, logical design and physical design.
- DATABASE directory
- The same as the Library Reference workspace. It is the system directory that LIBRARIAN uses to manage information about a map library. Each map library has one database directory named DATABASE.
- data capture
- Operations that are required to encode data in a computer readable digital form (e.g., digitizing, scanning). See also data input.
- data conversion
- The translation of data from one format to another. ArcInfo supports data conversion from many geographic data formats such as DLG, TIGER, DXF, and DEM.
- data dictionary
- A catalog of all data held in a database, or a list of items giving data names and structures. Also referred to as DD/D for data dictionary/directory. Commercial RDBMSs have online data dictionaries stored in special tables called system tables.
- data encoding
- To apply a code to represent individual data or groups of data. .
- data integrity
- Maintenance of data values according to data model and data type. For example, to maintain integrity, numeric columns will not accept alphabetic data. See referential integrity.
- data model
- 1. The result of the conceptual design process. A generalized, user-defined view of the data related to applications.
2. A formal method of describing the behavior of the real-world entities. A fully developed data model specifies entity classes, relationships between entities, integrity rules and operations on the entities.
3. ArcInfo coverages and grids use a georelational data model, a hybrid data model that combines spatial data (in coverages or grids) and attribute data (in tables). Other data models used in ArcInfo include tins, images, and grid.
- data quality
- The degree of excellence exhibited by the data in relation to a correct portrayal of the actual phenomena.
- data set
- A named collection of logically related data items arranged in a prescribed manner.
- data standardization
- The process of achieving agreement on common data definitions, representation, and structures to which all data layers and items must conform.
- data type
- The characteristic of columns and variables that defines what types of data values they can store. Examples include character, floating point and integer.
- DATABASE INTEGRATOR (DBI)
- ArcInfo software's link to relational database management systems (RDBMS). DBI enables ArcInfo users to access existing commercial databases and take advantage of the power and capabilities of the RDBMS.
- database lock
- Locking is a mechanism by which database systems can prevent conflicting access to data when multiple users are making requests to the data. See also persistent lock.
- database management system (DBMS)
- 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, storage, retrieval, query, and manipulation.
- datum
- A set of parameters and control points used to accurately define the three-dimensional shape of the Earth (e.g., as a spheroid). The datum 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.
- DBI
- See DATABASE INTEGRATOR.
- DBMS
- See database management system.
- DBMS table
- See attribute table.
- DCW
- "Digital Chart of the World." The first
1:1,000,000-scale digital basemap of the world. The DCW contains topologically based vector data
digitized from the U.S. Defense Mapping Agency's Operational Navigation Charts.
- DDE
- Dynamic Data Exchange. An IAC protocol developed by Microsoft for
Windows-based applications. DDE allows one application to send messages to,
and get information from, other applications in Windows. This is specific to
Windows only (RPC, Remote Procedure Calls, is used in the UNIX environment).
DDE is supported in ArcView Version 2 for the exchange of data with other
business applications without having to convert the data or leave ArcView.
(See IAC.)
- DDL
- Data definition language. SQL statements that can be used either interactively or within programming language source code to define databases and their components.
- delineation
- The legal description of the locations of points that mark the boundaries of a cadastral parcel.
- DEM
- See digital elevation model.
- demand
- 1. In allocation, the potential for using a portion of the supply of a resource or commodity.
2. In spatial interaction, demand is the measure of the need for a particular type of service or goods that generates a trip to a destination. For example, the demand for a gallon of milk may generate a trip to a grocery store.
- demarcation
- The field measurements (e.g., land survey) that determine the physical locations of boundary markers of cadastral parcels.
- denormalization
- The process of restructuring a normalized data model to accommodate operational constraints or system limitations.
- densify
- A process of adding vertices to an arc at specified distances, without altering the arc's shape. Compare with spline and grain tolerance.
- descriptive data
- Tabular data describing the characteristics of geographic features. Can include numbers, text, images, and CAD drawings about features. ArcInfo stores descriptive data in feature attribute tables and in related tables. Also referred to as attribute data.
- destination
- In spatial interaction, the location of the end of a trip. For example, a shop or an office where a consumer or a worker is going. Destinations are represented as centers in a network coverage, as points in a point coverage, and as label points in a polygon coverage.
- differential correction
- A technique for increasing the accuracy of GPS measurements by comparing the readings of two receivers, one roving, the other fixed at a known location.
- digital elevation model
- 1. 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).
2. An elevation database for elevation data by map sheet from the National Mapping Division of the U.S. Geological Survey (USGS).
3. The format of the USGS digital elevation data sets.
- DGM
- Digital Geospatial Metadata. DGM was approved in June 1994 by the
Federal Geographic Data Committee (FGDC). DGM describes the specifications for
the content, quality, condition, and other characteristics of metadata (data
about data). The standard provides a common set of terminology and definitions
for the documentation of geospatial data. DGM establishes the names of data
elements and groups of data elements to be used for these purposes, definitions
of these data elements and groups, and information about the values that are to
be provided for the data elements.
- DIGEST
- The Digital Geographic Information Exchange Standard is produced
under authority of NATO's Digital Geographic Information Working Group. DIGEST
is a standard for digital geographic information which will enable
interoperability and compatibility among national and multinational systems and
users. DIGEST is composed of standards for two digital geographic formats:
ARC Standard Raster Graphic (ASRG) and vector relational format (VRF). ASRG is
very similar to ADRG and can be imported into ArcInfo as an ADRG file with the
ADRGGRID command. The ArcInfo VPFIMPORT and VPFEXPORT convertors will process
the VRF data.
- digital image
- [REMOTE SENSING, PHOTOGRAMMETRY, GRAPHICS] An image stored in binary form and divided into a matrix of pixels, each consists of one or more bits of information that represent either the brightness, or brightness and color, of the image at that point. .
- digital terrain model
- See digital elevation model.
- digitize
- 1. To encode geographic features in digital form as x,y coordinates.
2. The process of using a digitizer to encode the locations of geographic features by converting their map positions to a series of x,y coordinates stored in computer files. Pushing a digitizer button records an x,y coordinate. A digitized line is created by recording a series of x,y coordinates.
- digitizer
- 1. A device that consists of a table and a cursor with crosshairs and keys used to digitize geographic features.
2. Title of the person who uses a digitizing device.
- digitizing
- See digitize.
- DIME
- See GBF/DIME.
- directed network
- A network in which each arc has an associated direction of flow. Direction of flow can be determined by arc direction (e.g., each arc is digitized so that it is oriented downstream), a value in an item in the AAT, or through the use of a selection file.
- directory
- A computer term identifying a location on a disk containing a set of data files and other directories (subdirectories). Operating systems use directories to organize data. The location of a directory is specified with a pathname.
- direichlet tessellation
- The process of splitting up a study area such that all points in the sample area are grouped into tiles according to the minimum distance between them and a previously sampled point. Also known as Thiessen or Voronoi polygons.
- discrete data
- Geographic features containing boundaries: point, line or area boundaries.
- disk
- A storage medium consisting of a spinning disk coated with a magnetic material for recording digital information.
- diskette
- An inexpensive, low-capacity storage medium, usually measuring 3.5 inches in diameter, often referred to as a floppy disk.
- dissolve
- The process of removing boundaries between adjacent polygons that have the same values for a specified attribute.
- distance-decay function
- In spatial interaction, the mathematical representation of the effect of distance on the accessibility and number of interactions between locations. It can be either a power or an exponential function.
- distributed processing
- The placement of hardware processors where needed, instead of concentrating all computer power in a large central CPU.
- DLG
- 1. Digital Line Graph files from the U.S. Geological Survey (USGS), including data from the base map categories such as transportation, hydrography, contours, and public land survey boundaries.
2. The digital format standards published by USGS for exchanging cartographic data files and in which the USGS delivers Digital Line Graph data sets.
- DML
- Data manipulation language. SQL statements that can be used either interactively or within programming language source code to access and retrieve data stored in a database management system.
- domain
- In a database, the set of allowed values for a table column, for example all positive integers.
- DOP - Dilution of Precision
- Also Geometric Dilution of Precision (GDOP) [GPS] An indicator of satellite geometry for a constellation of satellites used to determine a position. Positions with a higher DOP value generally constitute poorer measurement results than those with lower DOP. Factors determining the total GDOP for a set of satellites include, to name a few, PDOP (Positional DOP), HDOP (Horizontal DOP), VDOP (Vertical DOP), and TDOP (Time DOP).
- 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 data sets can be stored in either single- or double-precision coordinates. 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.
- downstream
- In tracing, downstream is the direction along the arcs that is the same as the direction of flow. Direction of flow is determined by a user-defined convention. See also directed network.
- drape
- A perspective or panoramic rendering of two-dimensional features superimposed on a surface.
- drum plotter
- A device with a rotating cylindrical drawing surface and paper reels for plotting graphic images on a continuous roll of paper.
- drum scanner
- A device for converting maps to digital form automatically.
- DTM
- Digital terrain model. See digital elevation model.
- dual independent map encoding
- For the 1980 census, the U.S. Census Bureau produced Geographic Base Files (GBF) and Dual Independent Map Encoding (DIME) files, containing census geographic statistical codes and co-ordinates of line segments for most metropolitan areas. DIME files provide a schematic map of a city's streets, address ranges, and geostatistical codes relating to the Census Bureau's tabular statistical data. DIME was replaced by TIGER® for the 1990 Census.
- DXF
- Data Exchange Format. A format for storing vector data in ASCII or binary files. Used by AutoCAD and other CAD software for data interchange. DXF files are convertible to ArcInfo coverages.
- dynamic segmentation
- The process of computing the locations of events on linear features at run time based on event tables for which distance measures are available. Route-system features and event-handling commands provide the dynamic segmentation capability within ArcInfo.