I'm trying to calculate building setbacks using building footprint data. A building setback is the distance between a building and the edge of the lot line. (You can distinguish this further—garage setback and structure setback, but I won't complicate things.) The image below (red lines) shows the distance I am trying to get for one of the blocks as an example.

building setbacks

I have no idea how to start this. I think I need to turn the footprint and parcel polygons into polylines and break at vertices? I want to use the street center-line (green) as a sort of magnet so that the distance is calculated to the front of the lot instead of the back or side. I can ignore corner lots for the time being.

BTW, the parcels are also dissolved so it is just block structure (pic below). That means I just need to find the shortest distance between the footprint polygon and the edge of the block polygon.

block structure

If anyone has any clue, please let me know! This is for a class project. (And I'm using ArcGIS and QGIS.)

  • There was a similar post here which might be of some help.
    – Joseph
    Feb 17, 2015 at 11:08

1 Answer 1


First of all, manually construct a huge polygon around all your light gray parcels. Then erase the parcels from the huge polygon. Now convert the light grey parcels to lines.

Once you have these layers, select by location the lines of the light grey parcels that share a line segment with your erased huge polygon. Export these selected lines into a new layer.

Finally, run the near tool with your black polygons and the resulting lines. That's the distance you are looking for.

  • Thanks for the tip. I will try this, but my concern is that it doesn't seem to be replicable across, say, an entire city. And that's what I'm trying to do. Any ideas? Feb 18, 2015 at 10:41
  • If you want to do it with a hole city just make the polygon big enough to surround your city. I don't see what is the problem.
    – Albert
    Feb 18, 2015 at 11:12

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