A Method to Distinguish Real Landscape Change from Map Error During Map Comparison

R. Gil Pontius Jr. and Christopher D. Lippitt
Clark University 
School of Geography
950 Main St. Box 1151
Worcester, MA 01610
Phone: (508) 769-4980
Fax: (508) 793-8881
Email: rpontius@clarku.edu

Abstract 
This paper describes a method to assess uncertainty in the measurement of change among categories of land cover between two points in time. Our method acknowledges that  error is an inherent part of map production, so differences between maps can be due to both real landscape change and to map error. For example, if two producers create a map of the same location for the same time, we would expect there to be disagreement between those two maps due to producer error. If we compare two maps of the same location from different times, we would expect to see disagreement between the two maps due to two reasons: 1) producer error, and 2) true landscape change between the former time and the  latter time. Our method uses matrix algebra and the conventional error matrix to distinguish between disagreement due to error versus disagreement due to real landscape change. The technique is applicable to conventional accuracy assessment because it relies on standard probability theory. We illustrate the technique with maps of Anderson Level I categories from 1971 and 1999 in Central Massachusetts and find there to be a dominant transition from Forest to Built over the last three decades. The method also shows that a substantial portion of the difference in water and wetland can be attributable to map error.

Keywords: Accuracy, Change, Error, GIS, Uncertainty, Matrix

In: McRoberts, R. et al. (eds).  Proceedings of the joint meeting of The 6th International Symposium On Spatial Accuracy Assessment In Natural Resources and Environmental Sciences and The 15th Annual Conference of The International Environmetrics Society, June 28 – July 1 2004, Portland, Maine, USA.

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