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Tracts, Subdivisions and Sub-Regional Areas

Within counties, there are several important Census geographies:

  • Cosubs, County subdivisions. Cosub areas are maintained by the Census, but may be defined by the county.
  • Metro Statistical Areas are defined as urban areas organized around a core, with limits on the size of the population. They are a type of Core-Based Statistical Area.
  • Sub regional areas, SRAs, are defined by the County of San Diego. The Census bureau has no role in maintaining SRAs.
  • Census Tracts are areas of between 1,200 and 8,00 people, with a target of 4,000.

The shapefile for SRAs is available in SANGIS in the Subregional_Areas_2010 file in the Census category.

As you can see in the map below, all of these divisions align to tract boundaries. Each SRA is entirely contained in a single MSA and a single Cosub, and each tract is entirely contained in a single one of each of the larger regions.

However, these regions do not align with San Diego HHSA service regions. See the second map, part of the San Diego Chronic Disease Atlas, for an overlay of the HHSA regions with the SRAs.

Cosubs, MSAs, SRAs and Tracts

HHSA Regions vs SRAs.