Sunday, October 29, 2006

Census 2000, Voting Precincts, & Parcel Geocoding

Hoo boy do I have a lot of catching up to do, but I'll start with this...

Professor emailed a table to me containing app. 15, 000 addresses within Arlington, TX, and wanted to know:
  1. Voting precinct the address falls within
  2. Voting precinct centroid the address is closest to
  3. Distance between the address and the closest precinct centroid
  4. Various Census 2000 demographics for each precinct
This was a fun project that took no more than a couple hours. Here is what I did.
  1. Geocoded the addresses to the city of Arlington parcel boundaries. As discussed here, the increased accuracy is worth the extra effort than relying on street geocoding. StreetMap USA makes it super-easy, but the errors compound themselves. Match rate was above 95%. Very excellent. The Arlington parcel boundaries can be pulled down here.
  2. In ArcMap, spatially joined the voting precinct boundaries to the geocoded addresses. This gave me the precinct number for each address. The redistricting boundaries can be pulled down from the Texas Legislative Council's FTP server
  3. In ArcMap, used the Feature to Point tool to generate the precinct centroids.
  4. In ArcMap, used the Near tool to calculate the closest (nearest) precinct centroid to each geocoded address. This also provides the distance, in feet, as I projected the data in State Plane (feet).
  5. Pulled down the necessary Census 2000 stats from Factfinder and joined it to the block groups.
  6. In ArcMap, spatially joined the block groups to the voting precincts. This aggregates the demographics on the precinct level based on where the block groups intersect the precinct boundaries.
That's it.

During the first half of this semester, I am receiving as many political science-related data requests as city planning and earth sciences, which offer degrees and/or certificates in GIS.