What are the rules/guidelines for what the total population in a US census block group has to be to justify a split?

I'm wondering if the US Census Department has any guidelines about when to split a census block group into separate parts.

  • While geographical, this question about US Census policy has no GIS content.
    – Vince
    Aug 24, 2015 at 10:55

1 Answer 1


Taken from https://www.census.gov/geo/reference/gtc/gtc_bg.html

Block Groups (BGs) are statistical divisions of census tracts, are generally defined to contain between 600 and 3,000 people...


Most BGs were delineated by local participants in the Census Bureau's Participant Statistical Areas Program. The Census Bureau delineated BGs only where a local or tribal government declined to participate, and a regional organization or State Data Center was not available to participate.

And since block groups are based on blocks themselves, it may be worth looking at http://blogs.census.gov/2011/07/20/what-are-census-blocks/ which describes how those are automatically created via computer software every ten years (with exceptions for changes in between) and are in no way dependent on population, unlike groups or tracts.

Further, there's this pdf from the aforementioned program that gives criteria of between 1 and 9 groups per tract and tract boundaries must follow group boundaries, in addition to the 600/3,000 population criteria. This other pdf appears to be the instructions for the program, and it looks like software does some of the review (ie, population too high, this needs to be split, prompt user what to do, etc.).

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