What are Geographic Data?

In General

geometric objects: roads (lines?), intersections (points?), cities (areas?).
complex geometric properties:
- connectivity (between intersections, from one exit to the next)
- adjacency (counties to the left and to the right, roads joining at an intersection)
- order (sequence of landmarks, cyclic order of roads at intersection)
- metric information (cardinal directions, lengths).
geometry includes directions of roads (one-way streets!) and additional information such as widths of bridges, heights of tunnels.
multiple reference systems: geodetic coordinates, mileage along roads, postal addresses.
multi-dimensionality: primarily surface (2d), but also overpasses (2d with co-dimension 0), temporal changes.
multiple representations: roads may be seen as 2-dimensional objects (e.g., when driving) or just as lines (e.g., at the planning level).
combination of spatial and non-spatial data: roads have a geometry, but also non-geometric attributes such as road classification, name, toll.
queries to retrieve alphanumeric information and spatial information to be displayed graphically (maps, images, etc.)
complex spatial analyses: routing of cars (shortest paths, with various interpretations of "shortest", e.g., distance, time, gas, toll).

Automated Mapping / Facility Management (AM/FM)
- Spatial data of a specific kind (utility lines), primarily graphic-oriented.
Environmental Monitoring
- Remote Sensing: recording reflection of various kinds of radiation from the earth's surface; no concept of "objects"; fixed resolution (e.g., 30*30 meters).
Census
- importance of topological information, primarily about spatial inclusion (who lives in which district)
- clear identification of objects (buildings) and their boundaries (administrative boundaries of parcels, towns, etc.)
- parcel based (partition of the earth's surface) additional information such as roads, different kinds of spatial subdivisions (school districts, voting districts).

graphics is concerned with the display of data (visualization, color)
geometry deals with mathematical properties (topology, metric, order)
- geometric information enables the users to maintain a consistent geographic database and to ask complex spatial queries.

Different from other spatial databases such as CAD/CAM, VLSI, image, and multi-media databases.

Last updated on July 26, 1996.