Geospatial Glossary

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1 API [programming] Acronym for application programming interface. A set of interfaces, methods, protocols, and tools that application developers use to build or customize a software program. APIs make it easier to develop a program by providing building blocks of prewritten, tested, and documented code that are incorporated into the new program. APIs can be built for any programming language.
2 ArcGIS Online A web-based system for sharing, finding, and using maps, layers, and services. ArcGIS Online includes a set of basemaps, map layers, and tools published by Esri for use inside ArcGIS products.
3 Authentication [computing] The process of validating the identity of a user who logs on to a computer system, network, or Web site.
4 Dataset [data management] Any collection of related data, usually grouped or stored together.
5 Feature class [ESRI software] In ArcGIS, a collection of geographic features with the same geometry type (such as point, line, or polygon), the same attributes, and the same spatial reference. Feature classes can be stored in geodatabases, shapefiles, coverages, or other data formats. Feature classes allow homogeneous features to be grouped into a single unit for data storage purposes. For example, highways, primary roads, and secondary roads can be grouped into a line feature class named "roads." In a geodatabase, feature classes can also store annotation and dimensions.
6 Absolute georeference The referencing in space of the location of a point using a predefined coordinate system such as a national grid or latitude/longitude
7 Absolute Measurement a level of measurement higher than ratio where the unit of measurement is not an arbitrary decision, so the numbers cannot be rescaled and retain their meaning. Probability is an example of an absolute scale.
8 Absolute Orientation Scaling,leveling and orientation to ground control of a stereo pair of aerial photographs during the photogrammetric setup process.
9 Accuracy closeness of a measurement to a value thought to be true; repeatability can be estimated by repeated measurement, measured by variance for continuous measures; accuracy of classification for categories can be summarized by a misclassification matrix when compared to a survey of greater accuracy.

Source : Exploring Geographic Information Systems by Nicholas Chrisman
10 Acetate Overlays A nonflammable plastic sheeting used as a base for photographic fils or as a drafting base for overlays where critical registration is not required.
11 Address Matching The ability to match an address component to its geographic location on the ground 
12 Aerial photograph Photograph taken from an aerial platform (usually an aeroplane), either vertically or obliquely.
13 Affine Transformation Coordinate transformation to convert map coordinates into database coordinates
14 Aggregation The process of combining smaller spatial units, and the data they contain, into larger spatial units by dissolving common boundaries and lumping the data together.
15 Airphoto A 9" x 9" photograph taken vertically downward from the air on 10" roll film. Airphoto images may be in the form of paper prints or transparent film. An airphoto includes significant horizontal displacement introduced by camera characteristics, tilt, nearness to the target scene, and variations in elevation of the target terrain.
16 Annotation Text on a drawing or map associated with graphic entities.
17 Application A program (software) or web mapping service designed to perform a specific task. Examples include word processing software, database programs, and mapping tools. GIS applications can be used to solve problems, automate tasks, and generate information within a specific field of interest. They can also be used to search, analyze, and map data to answer particular questions.
18 Arc An ordered string of vertices (x, y coordinate pairs) that begin at one location and end at another. Connecting the arc’s vertices creates a line. The vertices at each endpoint of an arc called nodes.
19 ArcCatalog [software] ArcCatalog is an application in the ArcGIS suite used to manage geographic data – similar to windows file explorer.
20 ArcGIS  A collection of software products developed by ESRI. This includes ArcView, ArcEditor, and ArcInfo levels of functionality as well as the main applications of ArcMap, ArcCatalog, and ArcToolbox.
21 ArcGIS Server Web service [ESRI software] A Web service processed and executed from within an ArcGIS server. Each Web service has a distinct HTTP location (URL). Web access is enabled by default for all ArcGIS Server services, but can be turned off by an administrator.
22 ArcGlobe [software] ArcGlobe is a global three-dimensional visualization and analysis environment as part of the Esri ArcGIS suite (3D analyst), specializing in global datasets and larger study areas.
23 Area of Interest A user defined area (represented by a bounding box, circle or polygon). Often used as a filter in a query.
24 Aspect [GIS processing] Aspect is the slope direction on a terrain surface. Aspect is measured clockwise starting North as 0° to 360° North again with flat areas given a value of -1 (or 0 degrees).
25 Attribute The range of possible values of a characteristic; an attribute value is a specific instance of the characteristic associated with a geographic feature.
26 Attribute table [data structure] An attribute table stores non-spatial information in columns and rows about geographic data – similar to spreadsheets.
27 Automated Conversion The process of converting maps and drawings into a digital format while reducing or eliminating operator intervention. Scanning is one form of automated conversion. Heads-up digitizing via tracing a raster image displayed on a computer screen is another form.
28 Automated Mapping The use of computer graphics technology to produce maps. May include specialized CAD technology for digitizing and editing map features, and DBMS technology to produce thematic maps.
29 Axis A reference line in a coordinate system
30 Azimuthal projections Map projections in which the surface of the globe is projected onto a flat plane.
31 Backlighting During digitizing, refers to using digitizing tables which illuminate the map from below
32 Base layer A layer containing a variety of features often used for locational reference (e.g., section corners, political boundaries, and other major features) or to establish geodetic control which ensures geographic fidelity between data sets in the GIS.
33 Base map Mapped data which seldom change and which are used repeatedly for locational reference and control. It also establishes the lowest common denominator for map scale, coordinate system, and projection for other maps in a GIS database. Contrast with thematic map.
34 Basemap A map containing geographic features used for locational reference. Roads are commonly found on basemaps.
35 Best Practice or Best Management Practice A recognized technique, method, or process related to developing, documenting, managing, sharing, distributing, or utilizing geographic data or applications which promotes consistency and compatibility of the data. It is a reflection of what the GIS community has found to work most efficiently and effectively. Best practices or guidelines may evolve into standards when officially adopted and mandated.
36 Bit Maps A pattern of bits  on a grid stored in memory and used to generate an image on a raster display