Census Tracts (2010)

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

Countywide	Downtown
Census Tracts 2010	Zoomed at Downtown LA

What is unique about LA County’s data?

1. It  is clipped to the ocean boundary.  Raw Census data includes a 3 mile buffer into the ocean, which impacts cartography.
2. 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

General Area	Zoomed in

How was this data created?

This data was downloaded from Census Bureau website: http://www.census.gov/cgi-bin/geo/shapefiles2010/file-download and clipped to the County Boundary using  ESRI’s ArcGIS Desktop.  Two new fields were added in census tract data – area in square feet and area in square miles. This dataset has unique identifier field “GEOID10” for each record and the census tract number fields “CT10” and “LABEL” (6-digit number and 6-digit number with decimal point, respectively).

Download/Access the data

• 2010 Census Tracts.lyr (ArcMap 10 Layer File) – for LA County staff with access to the GIS Repository
  
• LA County updated Tract File – ct2010.shp (zipped shapefile)
• Original 2010 Census Tract File – ct2010_original.shp (zipped shapefile) – this is the original file before the changes to Tract 8002.04 and 1370.00