Much of the recent research concerning the use of GIS has revolved around data quality. Types of errors inherent in GIS data layers, and also errors that may be produced through the creation and manipulation of data layers have been identified. Definitions of these errors, and observations of how these errors occur have been offered. However, the majority of the research is qualitative. It is known that positional variation is produced through differing interpretations and generalization of points, lines, and polygons, but it is not known to what extent. This information would be extremely helpful in allowing the user of the information to fine tune the application, based on the accuracy of the data. Providing this type of information is the goal of this research. Quantitative analysis of the results of a series of experiments will give a numerical range of possible positional errors produced through database creation via aerial photo interpretation.