Cartographic Guidelines for Geographically Masking the Locations of Confidential Point Data

Abstract

This research proposes cartographic guidelines for presenting confidential point data on maps. Such guidelines do not currently exist, but are important for governmental agencies that disseminate personal data to the public because these agencies have to balance between the citizens’ right to know, and preserving a citizen’s right to privacy.In an experiment, participants compared an original point pattern of confidential crime locations with the same point pattern being geographically masked. Ten different masking methods were tested. The objective was to identify appropriate geographic masking methods that preserve both the confidentiality of individual locations, and the essential visual characteristics of the original point pattern. The empirical testing reported here is a novel approach for identifying various map design principles that would be useful for representing confidential point data on a map.The results of this research show that only two of the ten masking methods that were tested yield satisfactory solutions. The two masking methods include aggregating point locations at either (1) the midpoint of the street segment or (2) at the closest street intersection. The cartographic guidelines developed from this research suggest a combination of both masking strategies. Future research should focus on the refinement and further testing of these, and other alternative masking methods.