Neither Here nor There: Using GIS to Integrate Data from Incongruent Geographic Areas

Jana Chavers, College of William and Mary
Laura C. Nixon, College of William and Mary
Kate C. Dykgraaf, College of William and Mary
Amin Vafa, College of William and Mary

Demographers often work with data that summarize populations living in pre-set geographic areas (e.g., census areas and school districts). In some cases it is necessary to summarize data describing two different types of geography to one common geographic unit. This is not always an easy task as geographic areas often have incongruent boundaries. For example, it is not possible to summarize block-group population characteristics to school districts by simply summing population characteristics of block-groups that lie partially inside those school districts. To overcome this problem, we developed a technique (using Geographic Information Systems) to assign population weights to the characteristics of block-groups that lie partially within a second type of geographic area. These weighted block-group characteristics can then be summarized to school districts reliably. We demonstrate how this is accomplished and use a variety of data to assess the accuracy of the our geographic weighting method.