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I'm using a shapefile of TIGER data provided by the Census Bureau for locating an individual's congressional district. In PostGIS I'm running an ST_Intersects query in order to take a (lat, long) coordinate and return the results set.

Of course, there are many points along the polygons that intersect both, but are not contained in either, hence the choice for ST_Intersects over ST_Contains.

Are there any real world examples of addresses that actually straddle two congressional districts? This edge case makes me suddenly nervous that I could be presenting users with the wrong district.

EDIT:

It appears that congressional districts might use census blocks which divide streets down the middle, so you technically should not have an address that bounds both. A follow-on question would be whether there are any known conflicts between a service's address geocoding and census mapping.

  • What would it mean if there were? That someone could vote twice?! You can be sure someone has already worked that out. Changing the question without changing the title is a bit of a bait-and-switch. GIS SE questions should ask one question. If you don't want to answer your original question, please edit the question to focus on your follow-on (which is unclear -- which service) – Vince Apr 10 '16 at 20:39
  • @Vince after asking the question, someone commented offline that possibly the districts are drawn via census blocks. This doesn't necessarily change the nature of the question, but does change the context in which it is asked. And of course it doesn't mean that someone could vote twice. We're dealing with my question of trying to find a voter's congressional district. While it's likely that state governments have figured this out, it's equally possible that I could get it wrong. Understanding the situation seems like a generally good idea. – Josh Smith Apr 11 '16 at 2:06

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