A

Attributes - information about each map feature stored in Tabular form.

C
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.

Ex. Contour lines connect points of equal surface value.


D
Dangling node - the endpoint of a dangling arc not connected to another arc.

Data type - The characteristic of columns and variables that defines what types of data values they can store. 

(Ex. Numeric – for numeral characters only, and Character (Char) – for all other keyboard characters).

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. For example, a series of x, y and z points that have a virtual layer draped over their surface can form a 3 Dimensional Image. Digital elevation models are typically used to represent terrain relief. Also referred to as 'digital terrain model' (DTM).

Digitizing – Paper maps can be used to create a digital map, for example, by using a digitizing mouse to trace the paper map. Lines can also be added to an existing digital map.

Dissolve - the process of removing boundaries between adjacent polygons that have the same values for a specified attribute.


F

Features - real life objects or things that are represented on digital maps. They can be modeled by: Points - locations of Lamp Posts, Lines - streets, or Polygons - a lake or land parcel.

Feature Attribute Table - a table used to store attribute information for a specific feature class. 

G

Geocode - the process of identifying the coordinates of a location given its address. For example, an address can be matched against a TIGER street network to determine the location of a home. Also referred to as address geocoding.

Global Positioning System (GPS) - a system of satellites and receiving devices used to compute positions on the Earth. GPS is used in navigation, and its precision supports cadastral surveying. Readings of points can be taken, for example, with GPS receivers.

I

Interpolation – A mathematical formula that estimates, for example, z values of a surface at an unsampled point based on the known z values of surrounding points.

M
Map Extent

1. The rectangular limits (xmin,ymin and xmax,ymax) of the area of the Earth's surface displayed on a map. A map extent is usually specified in the coordinate system of a map layer or other geographic data set used. 

Map Projection - A mathematical model that transforms the locations of three dimensional features on the Earth's surface to locations on a two-dimensional surface. Some projections preserve shape; others preserve accuracy of area, distance, or direction. Any such map representation distorts some parameter of the Earth's surface be it distance, area, shape, or direction. 

Meridian - a line running vertically from the north pole to the south pole along which all locations have the same longitude. 

N
Nodes - points that represent the beginning and ending of a line feature, for example. 

O
Overshoots - the portion of an arc digitized past its intended intersection point with another arc. To correct an overshoot the line segment needs to be snapped to the arc for which is was intended to snap too.

P
Pan - to move the viewing window up, down, or sideways to in order to view map features outside the current viewing window. 

Parallel - A horizontal line encircling the Earth at a constant latitude. The Equator is a parallel whose latitude is 0. Measures of latitude range from 0 to 90 north of the Equator and from 0 to -90 to the south.

R
Remote Sensing - acquiring information about an object without contacting it physically. Methods include aerial photography, radar, and satellite imaging.

Route - Routes usually define specific paths along a line segment or multiple line segments. For example, the portion(s) of a street that are traversed in order to get from location “A” to location “B” including the direction traveled.

S
Satellite Image - a picture of the earth taken from an earth-orbital satellite. Satellite images may be produced photographically or by on-board scanners (e.g., MSS).

Snapping - the process of moving a feature to coincide exactly with coordinates of another feature within a specified snapping distance, or tolerance.

Spatial Data - information about the location and shape of, and relationships among, geographic features, usually stored as coordinates and topology.


T

Tile - the spatial unit by which geographic data is organized, subdivided, and stored in a map library. Tiles subdivide the area covered by a map library and organize the library data by location (e.g., counties might be the tiles in a statewide database). A tile can be a regular, geometric shape. For example, in an undefined area a tile is typically a square portion of a larger map.


U
Undershoots - An arc that falls short of its intersection point with another arc. A legitimate example of an undershoot is a road (line) segment that represents a cull de sac.

Universe Polygon - the first record in a polygon attribute table, for example. It represents the area beyond the outer boundary of the coverage. It's the only polygon that never has a label point, and so has a User-ID value of 0. Its area equals the negative sum of all the polygons in the coverage. Also referred to as the external polygon.


V
Vertices - points along a line between the beginning and end node of a line. Vertices help to shape a line.