Properties of Geographic Data

• Geometry
• Distribution of objects in space
• Temporal changes
• Data volume

Geometry

• Primitive geometric objects (e.g., point, line, area)
• Complex geometric objects are built from basic ones
• Composition of primitive objects is partially ordered, not hierarchical (a point can be a corner of several areas)

Distribution of Objects in Space

• Geographic objects have a distinct identity
• Geographic objects may be completely or partially included in others
• Geographic objects from different classes overlap (land parcel, census block, school district, land use zone)
• The spatial extent of different geographic objects varies dramatically
• The density of objects varies across geographic space
• Geographic data may be organized in "thematic layers."

Temporal Changes

• The spatial distribution changes through addition and deletion
• The geometry of individual spatial objects changes (roads, rivers, parcels)
• Access to previous values may be necessary (legal aspects, requiring at least 2 time concepts: time of event and time of recording)
• Long transactions (new road, selling a parcel).

Data Volume

• GIS are very large collections of data
• Individual records are small, but contain many references
• Redundancy is often unavoidable
• Relatively constant data volume per organization.
  
  
  
  

Last updated on July 26, 1996.