Block Groups with very large populations

I'm looking at ACS 5YR 2019 vintage and its B01001e1 population estimates.

Population looks nicely distributed between  few hundred and a few thousand people.

Except, there are several block groups with more than 20,000 people and a few with more than 50,000.

Does anyone know a rule or definition that explains these extremely large block groups?

For example:
                          380170405002 Cass County, North Dakota - outside Fargo
                          481576729001 Fort Bend County, Texas - outside Houston
                          121199112001 Sumter County, Florida - includes The Villages
                          060730187001 San Diego County, California - includes San Diego

Parents
  • Population growth over the previous decade?

  • The estimate itself rather than growth   ( using ACS_2019_5YR_BG.gdb )

    A histogram of population (B01001e1) has a major right skew 

    because there are 3.9 million people in the 13 largest blockgroups:

    blockgroup           B01001e1
    060770035003     20430
    060730133141     22349
    060730187001     38754
    060770052063     20030
    121199112001     39928
    120310144121     20123
    120950167301     34230
    120950168071     20252
    120950167041     24985
    120950171032     22381
    130510107001     25166
    380170405002     42175
    481576729001     59947

  • How large were these block groups in 2010? That's what I'm asking. Certainly a development of 20,000 or more is conceivable in a 10-year period

  • Fort Bend county is one of the fastest growing counties in the USA. I haven't checked all the others you mentioned, but at a glance they are all urban areas. Why not population growth since 2010, when the block groups were last delineated?

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