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Track: Application Development Techniques
Erik Shepard
The University of Georgia
Chicopee Complex Suite 2076
1180 East Broad Street
Athens, GA 30602-5418
Telephone: 706-542-6293
Fax: 706-542-6535
E-mail: shepard@itos.uga.edu
Doug Atkinson, Anita Russo
Interpolation of Population-Related Polygon Data
Defining Issue: Polygon data are frequently interpolated based upon weighted area; however, this has the deficiency of assuming that the data are uniformly distributed. If this is not the case, as with population data, a different weighting method needs to be used that takes into account spatial distribution. GIS Solution: Information Technology Outreach Services at the University of Georgia has developed the Georgia 100 Geographic Information System that, among other things, provides a method that better reflects spatial distribution when interpolating population related data. Methodology: Areal interpolation weights data values for a partial polygon proportionally to the ratio of partial polygon area to complete polygon area. For population-related data, however, knowledge of the actual populations of subpolygons comprising the original polygon can be used to approximate varying density. The areal weight for each subpolygon is first calculated and then used to weight the associated population value.
The weighted populations are then summed and the ratio of partial polygon population to complete polygon population is calculated. Finally, the population ratio is used to interpolate the population-related data value of interest, such as mean income, for the original polygon. This improved method assumes that the data are uniformly distributed in the subpolygons, which is a better assumption than uniform distribution in the original, larger polygon. Increasingly fine resolutions of population data will better approximate varying population density in the original polygon. Software: The method for population-based interpolation was written in ARC Macro Language and runs under ArcInfo and ARCPLOT. The purpose of this paper is to address the appropriateness of using population information to interpolate population-related data for partial polygons.
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