In 1992 Dr. Lance Waller, currently an Associate Professor at Emory University in Atlanta and author of Applied Spatial Statistics for Public Health Data, introduced a new statistical test of focused clustering -- clustering in the vicinity of potential sources of risk. Dr. Waller's analysis, published in the journal Environmetrics, used the test to investigate the clustering of leukemia incidence in upstate NY around waste sites contaminated with TCE, a solvent used to clean metal parts.

At the time, digital cartographic tools and data were in their infancy and Dr. Waller geolocated the hazardous waste sites manually using printed maps from the United States Geological Survey (USGS).

In light of improvements in geographic information systems, global positioning systems and cartographic data availability Dr. Waller decided to revisit his analysis beginning with an evaluation of the accuracy of his original geolocation efforts. Dr. Waller contracted ZevRoss Spatial Analysis to conduct this initial assessment.

Improved Geolocation Achieved by Overlaying Modern GIS Data

As part of the accuracy assessment a wide variety of data types from several different sources were used, starting with updated USGS digital raster graphic (DRG) layers similar to those used by Dr. Waller initially. The locations were verified by overlaying 1996 raster quadrangles from the New York State Department of Transportation on top of USGS DRG layers. In the final step, the locations of the facilities were pinpointed by overlaying the digital Department of Transportation maps with a series of high resolution aerial photos. Dr. Waller plans to use the updated facility locations in a re-analysis of his 1992 paper.

Final Overlay of Map Layers

This map is an example of the maps produced for Dr. Lance Waller. It is an overlay of the two map layers pictured below -- a Department of Transportation digital raster graphic and digital orthophotos. Note that the DOT graphic has been stripped of its white background and, for visual clarity, the black lines have been replaced with cyan lines.

New York Department of Transportation Digital Raster Graphic (left); New York State Digital Orthophotos (right)

Source for the orthophotos: New York State GIS Clearinghouse

© 2008 ZevRoss Spatial Analysis