• Points, lines and polygons
  • choice often determined by scale, level of detail and accuracy
  • degree of difficulty and accuracy usually increases with polygons
    • polygons must be enclosed
    • what is topology?
      

Two ways to represent geographic features:

• Vector - defined by series of x,y coordinates (connecting the dots)

- multi-attributes associated with features
- much of analysis performed by attribute tables

• Raster - matrix of cells or pixels; each layer represents one attribute

- best used for continuous phenomenon such as vegetation, precipitation
- much of analysis performed by combining new layers

Functional Feature and Surface Types:

• Discrete - actual location can be pinpointed
  • cities as points, streams, parcels, fire hydrants, species, etc.
    
    
• Continuous - phenomenon occurs in all areas
  • geographic expanse called surfaces
  • contain numeric values (raster data)
    • depth of ocean, precipitation, temperature, elevation, slope (steepness)

- use series of sample points to "interpolate" areas between (isolines)
- spectrum or enclosed areas (polygons)

• Summarized by Area - represents counts or density with area (called choropleth maps)
  (businesses by area code, vegetation types, demographic data)
  

Index