Wednesday, March 14, 2007

Get your real, live examples!

After only posting screenshots for the past few days, it is time to share some real, live KMZ files. I'm going to share 3 states worth of data: California, Massachusetts, and Wyoming. Before I share links to the actual files, I want to be sure to share some important definitions, data sources, and notes.

What is mapped?

  • I wanted to start simple: the following KMZs map the "Total Population" variable from the 2000 Census, broken out at the County Subdivision level. The height of each subdivision is equal to 1 meter for every 10 people. The colors also represent population, but use the state's max county subdivision population as the denominator, meaning they are only relevant within the state, not comparable across states. The largest subdivision will be bright red and the small ones will be white. I'm experimenting with this to try and get data on two levels - national and state.
Where is the data from?
  • While I could have gotten the data from the FactFinder, I got the actual Total Population variable data from National Historical Geographic Information System (NHGIS). This system is powerful because, among other things, it lets you download the data for the entire US at once. The citation for this data is as follows:
    • John S. Adams, William C. Block, Mark Lindberg, Robert McMaster, Steven Ruggles, and Wendy Thomas, National Historical Geographic Information System: Pre-release Version 0.1 Minneapolis: Minnesota Population Center University of Minnesota, 2004.
  • The County Subdivsion boundary files came from a Census website: 2000 County Subdivisions Cartographic Boundary Files.
    • The Census boundary files include data the denotes cut outs when a polygon should not cover an area. These are denoted with a -99999 ID in the Census boundary files. While I read these in, I have not decided the best way to handle them so that data is not represented here: in other words, some of the polygons may inappropriately cover an area.
  • The actual population (in people) is listed for each County Subdivision in the name for each polygon. The number listed here is the actually population divided by 10, which is the height of the polygon in meters.
  • This is a preliminary release.
  • I license the use of these files under Creative Commons and Commercial use of the data is prohibited by NHGIS. The data can be gotten for other ways, so Commercial use is not out of the question in the future.
  • Turn off Terrain for best viewing.
  • Rotate, fly around, change the viewing angle to get a real sense of the visualization!
  • I do not warrant in any way, the accuracy of these maps. Use at your own risk.

Maps of Total Population (people) from the 2000 Census by County Subdivsion:
Please pass along any feedback/thoughts/inquires via comments!


Anonymous said...

This visualization technology is powerful stuff!

Great work, and thanks for the files!

Anonymous said...

This is very nice work. I really appreciate making your work available on RubyForge, as well. I checked the code out of svn last night and noticed a parse error, a not well-formed (invalid token) when rendering the test kml files on GE. After an all-too-brief look, it might the cdata tag format.

aidan said...


Thanks for the feedback. I'm sorry to say that I haven't posted the code yet - the code at Ruby KML isn't mine. I hope to share the code soon - is Ruby Forge the best place?