Enhancements to GIS Tools and Methods for
Mapping American Community Survey Estimates and Data Quality Information

In the previous project entitled GIS Tools for Mapping American Survey Estimates and Data Quality Information, we developed several versions of an ArcGIS extension (ACS Mapping extension) to handle and map ACS estimates with data quality information. The current project is a continuation of the previous project in extending the capabilities of the ACS Mapping extensions. Several new mapping functions have been added to the extension to facilitate the mapping and analysis of ACS data.

This project is also partially funded by the U.S. Census Bureau contract order # YA132312SE0387 for the period September 4, 2012 C December 12, 2013 (Contract Officer/Technical Manager: Dr. Nancy Torrieri). The contract was awarded to David W. Wong at George Mason University.

We intend to keep the information of the first project on the website unchanged. The new information is very much limited to the page to download the ArcGIS extensions. The most updated information about the new extensions is can be found in the release note and the documentation/user manual.

New: August 2013

Class Separability Classification Method

Besides developing the ACS Mapping extensions for ArcGIS, we recently developed a new map classification method for choropleth mapping to incorporate data reliability information. In mapping ACS data, estimates are assigned to different map classes, portraying the impression that they are different, but in fact they may not be statistically different. Our proposed classification method looks for class breaks to maximize the likelihood that estimates are significantly different if they are assigned to different map classes. A tool that works partially with ArcGIS has been developed and can be downloaded from the "Download" page of this website. The literature page has also been updated with publications resulted from this project and other pertinent articles.

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 4, 2012 C December 12, 2013, Technical Manager: Dr. Nancy Torrier