Tried searching for this information elsewhere and couldn't find a clear answer in the TIGER documentation, so I thought I'd turn to you good folks.

Obviously, congressional districts can cut across counties and 'cities', but which census geography boundaries do they preserve (if any)? Tracts? Block Groups? Blocks?

I suppose I'm most interested in learning what is the largest type of census geography whose boundaries are preserved by congressional districts in every case.

Thanks in advance!


While some districts may follow block group, tract or even county boundaries, many of them (probably most -- might depend on the individual state) were based on block-level data. Since the districts have to be drawn based on Census data, and since the smallest level of geography the Census Bureau uses is the block, there should be no districts that violate block boundaries.

EDIT: I've added a diagram from a Census Bureau Redistricting PDF of the nestability of various geographies. As you can see, blocks are the only geography that are guaranteed to nest within Congressional Districts (CDs).

enter image description here

  • Awesome, authoritative answer. I mean, that makes the volume of data I have to work with more ... 'voluminous' ... but still, good to know! Thanks @nmpeterson ! – dubhousing Mar 22 '13 at 21:08
  • Yeah, blocks can be a real headache to work with, just because they make everything run so slowly. Glad to help. – nmpeterson Mar 22 '13 at 22:44

US census districts changed over time as did counties boundaries. I don't know specifically which census are you looking for but here you can find shapefiles with state/counties change over time

  • I appreciate that, and I realize where the shapefiles reside, but that doesn't quite answer my question. While districts and county boundaries change over time, I'm specifically asking if congressional districts preserve the integrity of any geographies below the city/'places' level: i.e., is there a geography-level (tracts? block groups? blocks?) whose boundaries the congressional districts boundaries do not cut across? – dubhousing Mar 22 '13 at 20:32

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