Adding external properties to TopoJSON file of counties

Question

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I'm trying to add external properties to a topojson file, us-counties.json (made with us-atlas using make topo/us-counties.json). I'm working off this example. But my resulting topojson file us-counties-with-population.json has no properties at all.

My call looks like:

topojson --external-properties data.csv \
  --id-property id_county \
  --properties population=+percent_population \
  -o us-counties-with-population.json \
  -- us-counties.json

and my data looks like (head -n5 data.csv):

id_county,county_name,percent_population
01003,"Baldwin County, Alabama",9.71576144493279
01043,"Cullman County, Alabama",6.734653334216277
01051,"Elmore County, Alabama",7.095232589509385
01069,"Houston County, Alabama",9.857459440234194

I'm using topojson v1.2.2. I think I might be missing something related to how the ids are matched, but I'm not sure what it is.

Answer 1

Very nice question, I spent an hour on this problem spinning my wheels. It turns out the External Properties section provides a simple example which uses the reference id FIPS as the id.

You should be able to use your csv with one simple modification. Rename id_county to FIPS. Next specify your external resource with the -e flag.

-p name=COUNTY,name=STATE,area=+SQUARE_MIL,population=+percent_population  -e data.csv

Answer 2

This answer worked for me: How to add properties to topojson file?

In your case the call would look like:

topojson -o us-counties-with-population.json -e data.csv --id-property=id_county,id -p properties population=+percent_population -- us-counties.json

Note: I'm assuming the id-property of your topojson file is id.