Census Tracks

[travisweiland@gmail.com]

Has anyone found census tracks in a json shape file and loaded it into CODAP with spatial data? I would like to graph some data that is unitized by census track so teachers can explore the data but I am struggling to put all the pieces together. Any help would be greatly appreciated.

[Bill Finzer]

Hi Travis,

Here is one just for California. I’ve never tried to make one for the whole U.S. It would be very large, of course.

Bill

[travisweiland@gmail.com]

Thank you. That is exactly the type of thing I am trying to do just for NC currently. If I am following what you did in your file it looks like you are have census tracks built into CODAP now that I can just use the lookupbykey function to add to a data table that has a Census Track variable with the numerical census track numbers. Is that correct or did you do some other magic in the background I am missing?

[Bill Finzer]

No, we don’t have census tract boundaries available, just the boundaries listed in the screenshot of the Variables menu in the formula editor. Plus, you would probably want a lot more than just the boundaries, right? I don’t remember where I got the CA data long ago. Sorry about that.

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[Dan Damelin]

Here’s a CODAP doc with NC census tracts.

https://codap.concord.org/releases/latest/static/dg/en/cert/index.html#shared=https%3A%2F%2Fcfm-shared.concord.org%2FrPsp6ogNPu0J6ZzzYj0p%2Ffile.json

To make this I searched the web for NC census tracts geoJSON, but could not find that. I was able to find shapefiles, which were here.

Then I opened this great tool (mapshaper.org) for simplifying and converting between various boundary file types. I uploaded the files that I had downloaded, clicked “simplify” and used the slider to reduce file size, and then “export” to save as geoJSON. Then you can just drag the geoJSON into CODAP and join tables based on one of the identifiers (assuming your data has one of those identifiers for linking).

[travisweiland@gmail.com]

Thanks Dan that is super helpful. One more quick follow-up question. When I go to reduce the file size to download as a geoJSON is there a ballpark file size you all recommend to work well with CODAP?

[Dan Damelin]

I don’t have a target file size, but smaller is better. What I generally do is move the % slider until I start to see a loss of detail in the borders. It’s amazing how much info can be thrown out and have almost no visual change in the boundary definitions. I’m quite impressed with their algorithm for simplifying shapes.

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