Polygonal Data Formats

Standard GIS formats (ESRI Shape, MapInfo...) are commonly used to represent polygonal data.  However, there are no standards at all for the per-polygon attributes that go along with these datasets, so importing data (e.g. with VTBuilder) requires a manual step of mapping one set of attributes onto another.

• example of polygonal data with attributes: the GIS Data at the Charles Lathrop Pack Forest
  • a good, free, detailed dataset includes polygonal coverages for soil, lakes, and forest stands

There are some domain-specific polygon data formats, such as USGS LULC, which define a standard for their attributes and can therefore be understood directly by software.

USGS LULC (land use / land cover) files

• 37 land usage types
  • detailed description of each classification code is described in:
    Anderson, J.R., Hardy, E.E., Roach, J.T., and Witmer, R.E., 1976, A land use and land cover classification system for use with remotely sensed data: USGS Professional Paper 964, 28 p.
• LULC does not contain any information about species or ecosystem, so it's primary usefulness is to describe vegetation density
• for example, it can tell which areas are agricultural, but not which crop is growing there
• the 1:100,000-scale format is a 30' x 60' quadrangle, UTM-based
• can be read by VTBuilder and the the vtdata library
  • it turns out GIRAS (the underlying format of LULC) is not difficult to read
  • however, the map coordinates are in a strange format, "local UTM"
  • how to correctly convert these coordinates to lat-lon or actual UTM is unclear
  • one way is to use the four LULC corners as a guide, defining a "perspective transform"
    • found an algorithm for this in the book Digital Image Warping, pages 52-56
• format description
  • the entire format is documented in USGS Data Users Guide 4 (converted by me to HTML for your reading pleasure)

See also: Sources of Data for Distribution of Plants on Terrain