Lecture 3: Types of Data in GIS
Selections from Marc van Kreveld, Geografische Informatiesystemen, 1996.
Buttenfield, B.P. Treatment of the Cartographic Line. Cartographica, vol. 22(2): 1-26, 1985.
An example using Watershed data: http://maps.epa.gov:10000/iwimap/
Some categories seen in this example (you will find that Geographers like to categorize.)
Stevenís Levels of Measurement
Ordinal: ordered by pairwise comparison (e.g., occurrence order)
Interval: quantitative, but with arbitrary zero and unit (e.g., years)
Ratio: quantitative, with true zero and unit. (e.g., dollar amounts)
Note which transformations preserve the information in a measurement.
Types of maps:
Topographic: detailed representation of topography
Thematic: communicates distributions, etc.
- choropleth: reports values in zones (e.g. counties, not determined by data)
- area class map: shows zones of constant values (zones determined by data)
- isopleth map: shows surface via isolines (e.g. elevation contours)
- cartograms: mapping some other attribute to area but preserving relationships
Line maps vs Photo maps
Raster: grid of values vs Vector: points and line segments
Field: mathematical scalar field common to scientific measurements vs Object: representations of discrete entities
Data models will appear in different layers; Layers can be combined visually, or by explicitly calculating their overlay.
Types of spatial objects as represented in a GIS
- Point: 0D (e.g. town of Chapel Hill at national scale)
- Line: 1D (e.g. branch of a river or segment of a road)
- Area: 2D (e.g. county delimited by its boundaries)
- Surfaces 2 1/2D (e.g. elevation or other scalar fields)
- Volumes (areas over time) 3D (e.g. subsurface geology in oil exploration)
Objects have attributes (names or values), and reflect some entity in reality.