This project is partially funded by the U.S. Census Bureau contract order # YA132310SE0580 between September 1, 2010 to June 30, 2012 (Technical Manager: Dr. Nancy Torrieri). The contract was awarded to David W. Wong at George Mason University.

Problems and Issues:

- Different from decennial census data, data gathered by the American Community Survey (ACS) have higher degree of unreliability. For each estimate in the ACS data, the Census Bureau provides the margin of error (MOE), an indicator of the reliability of the estimate. Using ACS data should take into consideration of the MOE
- Most mapping processes assume the data are accurate and the spatial patterns revealed by maps are true. These assumptions are invalid when using ACS data in mapping and in GIS. In addition, ACS data have a structure different from decennial census (due to the inclusion of MOEs). Using ACS data in GIS is not as straight-forward as the decennial census data

Solutions and Results:

An ArcGIS extension was developed to address some of the above issues.
- The extension includes detailed instruction to download ACS data and associated boundary data to be used in GIS.
- The extension include a tool to join downloaded ACS tables and census boundary shapefiles.
- Several mapping designs are developed in the extension. These designs facilitates the inclusion of reliability information when mapping ACS data. These designs also help readers determine if differences in ACS estimates are real or due to sampling error.
Because many users are using different versions of ArcGIS (9.3 and 10), and different versions of ArcGIS are not backward compatible, two versions of the extensions were developed.
For All Inquiries: David W. Wong, Geography & Geoinformation Science, George Mason University, Email: dwong2@gmu.edu Tel: 703-993-9260
Funded by the U.S. Census Bureau, Period of Performance: September 1, 2010 – December 31, 2011, Technical Manager: Dr. Nancy Torrieri