Merging Census Tract Data into NYC Council Districts

378
4
04-15-2019 01:38 PM
JanetHandal
New Contributor

I want to combine census tracts found within New York City's Council districts and find the average Participation rate. I have the census track and NYC council districts shape files and the table with the participation rates.  I have joined the participation rates census tract shapefile. I think the next steps are Intersect, then Dissolve, but would appreciate help figuring this out.  Thanks!

0 Kudos
4 Replies
ColeAndrews
Occasional Contributor III

Janet Handal‌ Are the council districts built on census tract geography? More specifically, can a council boundary run through the middle of a tract, or is a tract always in 1 council district?

This can change the way to go about getting the values.

0 Kudos
JanetHandal
New Contributor

Thanks for getting back to me. The census tracts can be split into 2 or more council districts.

0 Kudos
ColeAndrews
Occasional Contributor III

Got ya. There are several ways to go about it. How do you want to handle the tract participation info when it spans multiple council districts?

Often time, for overlaying polygons to polygons where there is not a direct relationship, we'll go with where the centroid falls. More specifically, you'd convert the tracts to centroids using feature-to-point tool, then spatial join the tract points to the council district, then calculate your participate rate by getting field statistics from the tract points joined to council district. With this method, a tract is only assigned to 1 council district, thus you have un-duplicated values.

You could use the intersect tool to split the tract polygons by the council districts, as you suggest. If you do not set any "ratio policies", the attribute values of the tracts are duplicated for each split of the tract polygon. If you have actual participation counts for the tract level, you could use the ratio policy setting to split the attribute value(s) and keep them un-duplicated. However, if your participation value is an aggregate (i.e., 50% participation in this tract), you can't really split/ratio that value properly with the intersect tool.

0 Kudos
JanetHandal
New Contributor

With the intersect tool, I each split of a census tract would duplicate the percentage of participation rate. I think this is reasonable given that what we are trying to do is get a figure for participation rate by council district. Someone else suggested using the areal interpolation tool. Will look at that too.

0 Kudos