Census Geography Background
The Census Bureau (http://www.census.gov/) maintains geographic boundaries for the analysis and mapping of demographic information across the United States. Every 10 years the Census Bureau counts the population of the United States as mandated by Constitution. The Census Bureau releases the results of this county as demographic data with geographic identifiers so that maps and analysis can be performed on the US population.
For a quick introduction to Census geography, click the thumbnail on the right which shows the relationship between Census Blocks, Block Groups, Tracts, and Counties.
For detailed information about the Census Geography, here are some other links:
- Geographic Shapefile Concepts Overview
- TIGER/Line Shapefile home page
- TIGER/Line Shapefile technical documentation
LA County Samples
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Countywide |
CSU LA |
 Census Blocks 2010 |
 Zoomed at CSULA |
What is unique about LA County’s data?
- It is clipped to the ocean boundary. Raw Census data includes a 3 mile buffer into the ocean, which impacts cartography.
- Each census blocks are assigned with the community name based on the 2011 redistricting unit community names.
- IMPORTANT! It has been updated to re-include Census Tract 1370.00, which the Census Bureau mistakenly merged with tract 8002.04. Note – until the Census Bureau releases updated population files this update will impact population mapping since population tables will not have 13700.00 (it’s population will be part of 8002.04 showing higher numbers than reality). Please see this post on the County Enterprise GIS about this. We have included the raw file for those who want to use it.
Maps showing what changed
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General Area |
Zoomed in |
 |
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How was this data created?
This data was downloaded from Census Bureau website: ftp://ftp2.census.gov/geo/pvs/tiger2010st/06_California/06037/ and clipped to the County Boundary using ESRI’s ArcGIS Desktop. A new field “COMMNAME” was added and populated with city and community names based on 2011 redistricting unit community names in the census block data. This dataset has unique identifier field “GEOID10” for each record, and the census tract and census block number combined field “CTCB10”, block group field “BG10” and census block number field “CB10”.
Download/Access the data
- 2010 Census Blocks.lyr (ArcGIS 10 layer file)- for LA County staff with access to the GIS Repository
- LA County updated Block File – cb2010.shp (zipped shapefile)
- 2010 Census Blocks (zipped original tiger shapefile) – CB2010_Tiger - this is the original file before the changes to Tracts 8002.04 and 1370.00