Thursday, March 22, 2007

New KMZ!

Today I'm going to share a KMZ of a new variable that I've been working on. I wanted to experiment with more complicated variables, beyond Median Household Income, to really push the flexibility of the code I'm writing. The migration variables of summary file 3 from the Census are fascinating and fit the bill. They allow one to understand how people are moving about the country and include quite a bit of granularity. I'm going to share 7 states worth of data: Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island, and Vermont. Before I share links to the actual file, I want to be sure to share some important definitions, data sources, and notes.

What is mapped?

  • There are many migration variables, but for this example I've chosen to use two. I used the Population 5 years and over: Total - P024001 variable which represents the number of people in 2000 over the age of 5 and used it to divide the Population 5 years and over: Different house in 1995 - P024003 variable. The resulting percent should represent the number of people, over the age of 5, who didn't live in the house they lived in during the 2000 Census in 1995. Put it simply, the percent of people who moved in the last 5 years. The migration data provides a much more detailed breakout of where the people that moved came from, which I hope to work further with.
  • The data is presented broken out by county: the taller, the more blue a county is in the file the higher a percent that moved - the shorter, the more green, the smaller percent that moved. The actual percent can be found in the description for each polygon, however it is multiplied by 1,000 there so the actual value is what is found in the description divided by 1,000.
  • In New England, the region in the provided KMZ, Tompkins County, New York has the max value at ~ 58%. This means that ~ 58% of people in Tompkins County moved since 1995. There are many counties at the low end: Hamilton County, New York is quite low at around ~30%, but so are Aroostook County, Maine and Orange County, Vermont, both around ~33%.
  • You'll also note how the counties are organized into folders within the KMZ file. This is a recent improvement to the KMZ generation process. I've also modified the code to follow the best practice of referencing repeated styles by ID (each polygon references a base style and only overrides what it needs to) - I thought this would save a lot on file size, but it didn't because ZIP was quite efficient at compressing the bits that were repeated again and again.
How about a quick tour of the map?
[YouTube seems to like to cut down the length of videos, so this may feel a bit choppy - not sure why it is doing this]

Where is the data from?
  • I downloaded the data from the FactFinder Download Center.
  • The County boundary files came from a Census website: 2000 County 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.
  • This is a preliminary release.
  • Turn off Terrain for best viewing.
  • Rotate, fly around, change the viewing angle to get a real sense of the visualization!
  • Commercial use of this file is prohibited. If you are interested in using this file commercially, please drop an e-mail to censuskml [at] [Gmail].
  • I do not warrant in any way, the accuracy of these maps. Use at your own risk.

Please pass along any feedback/thoughts/inquires via comments!

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