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Census Research Guide: Defining Your Community

Tracts & Blocks in San Diego

Defining your Community

The most difficult part of defining your Census geography is figuring out how Census designated geographies overlay with the streets and neighborhoods we know from everyday life.

You will need to determine what Census tracts, Block Groups and Blocks best match up with your community to find the Census data you need. These boundaries may not match up exactly with the official boundaries of your community, but street maps and Census Tract & Block maps will help you define an area that will work best for your research.

The San Diego Neighborhood Maps on the City of San Diego's website will help you identify the generally accepted street boundaries for your neighborhood.

For detailed street maps, check out the Thomas Guide San Diego County, Street Guide and Directory in the library (SSH Ref Desk G1528 S24 T5 v.2009) or use a web based mapping tool such as Yahoo! Maps or Google Maps.

For detailed online Census Tract, Block Group & Block information for 1990/2000/2010, you can use the Census Bureau Reference Maps in PDF  or use the mapping applications in American Factfinder. If you only need Census tract information, Social Explorer's Mapping function is a great option.

The PDF Block Maps are the most detailed maps available of Census geography. They are difficult to browse online, but make lining up street boundaries fairly easy. The Maps for 2000 are also available in paper in the SSH Map Collection (G4363.S24 s10 .U5) For earlier years, look for the maps in the Census Tract and Block volumes. (Maps are usually included in a back book pocket, or a separate folio shelved next to the volume.)


Don’t forget! Census tract numbers & boundaries may change over time. Check all your Census years before making a final decision on community boundaries. Remember, the farther back in time you go, the larger your Census tracts are likely to be.

Social Explorer (go to “maps” tab) is an online interactive mapping tool that can help you identify Census tracts and extract selected statistics for your community back to 1950. Social Explorer does not identify blocks or block groups, but does include streets and is an excellent way to quickly compare tract boundaries over time.