Attribute data: Descriptive information stored in a database about features located on a map

Base map: A GIS data layer of reference information, such as topography, road network, or streams, to which all other layers are referenced geometrically

Choropleth mapping: A map that shows numerical data for a group of regions by (1) grouping the data into classifications and (2) shading each class on the map

Connectivity: The topologiccal property of sharing a common link, such as a line connecting two points in a network.

Coordinate system: System with the components necessary to locate an object in two- or three-dimensional space (origin, unit distance, two axes)

Coverage: A digital version of a map containing both geospatial coordinates and attribute data.

Datum: A base reference level for the third dimension of elevation for the earth's surface; may depend on the ellipsoid, the earth model and the definition of sea level

Digitizing: The process in which geocoding takes place manually; a map is place on a digitizing tablet and a person traces the map features using a cursor or puck. The locations of features are automatically recorded in the computer.

Feature: Single entity that composes part of the landscape

Geocoding: Converting a location in geographic space to computer-readable form

Global Positioning Systems (GPS): System of satellites in orbit that allow their use by a receiver to decode time signals and convert the signals from several satellites to a position on the earth's surface

Layer: Set of digital map features (points, lines and areas/polygons) See also Theme

Map projection: A depiction of the earth's three-dimensional structure on a flat surface

Raster: A data structure for maps based on grid cells

Spatial data: Data that can be linked to locations in geographic space, usually via features on a map

Theme: "Overlay" -- a map of a particular feature or set of features (e.g., political boundaries, land use, population density)

Theme: A single spatial distribution or pattern (thematic mapping) See also Layer

Topographic map: A map type showing a limited set of features but including at the minimum information about elevations or landforms (ex. Contour maps)

Topology: The numeric description of the relationships between geographic features, as encoded by adjacency, linkage, inclusion, proximity or connectivity

Vector: A map data structure using the point or node and the connecting segment as the basic building block for representing geographic feature

Many definitions borrowed from Getting Started with Geographic Information Systems by Keith C. Clarke.