Mapping American community survey data

Abstract

Maps are a frequently used tool to portray the Census Bureau’s data and highlight spatial patterns that provide context and significance for the characteristics displayed. Maps provide visually what tables and other graphics cannot: a picture of the data, their distribution over geographic areas, and a means for interpreting the data shown by color, symbology, or explanation provided as annotations or as part of the map legend. The value of maps in enhancing an understanding of census data is well established as demonstrated by their frequent use in the media following the release of census data products. Mapping census data is common throughout government, academia, and the private sector. Casual users of maps of statistical data may not look past what is interesting visually to analyze the underlying data that a map depicts. However, that does not absolve the mapmaker of the responsibility for informing users of the statistical qualities associated with the mapped values. The Census Bureau set new standards for communicating the statistical qualities of estimates from the American Community Survey (ACS) by including information on the level of sampling error (specifically, margins of error) associated with every ACS estimate. Now, efforts are underway to develop an operational tool that will make it possible for geographic information systems (GIS) users to communicate this information through map products as well.