I'm using QGIS 1.8 on OSX 10.8.3.

I have a polygon shapefile of all of the US state legislative districts.

I also have a layer of points that are centroids of US Census Tracts, with a field for the population of the tract.

How do I generate a layer of points that are the weighted mean of each census tract point within each legislative district?

My hunch is to play with spatial joins and use fTools to do mean coordinates, but I'm not sure how to calculate the mean for each polygon instead of the whole layer itself.

Any thoughts?

  • You want the weighted mean of your centroids per district (geographically) or simply the mean of the population weighted by the number of tracts within a district? – Curlew Mar 31 '13 at 21:16
  • I believe the former. Each district contains many tract centroids, so I'd like the geographic mean center of population for each legislative district. – treznick Mar 31 '13 at 21:20
  • How about use the Vector > Analysis Tools > Mean Coordinates? – Alexandre Neto Apr 1 '13 at 9:06
  • Looking to answer a similar problem- I have output area population weighted centroids for the UK and I want generate higher level (local authority level) population weighted centroids from this data- doesn't seem to do the trick if I just find the mean coordinates-any help would be really appreciated- new to GIS! – user34617 Jul 16 '14 at 16:46
  • Hi Kate, welcome to SE. Instead of posting this as an answer, please create your own question thread and link back to this page. – GISKid Jul 16 '14 at 16:58

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