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A Comparison of Vector and Raster GIS Methods for Calculating Landscape Metrics Used in Environmental Assessments

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Abstract:GIS-based measurements that combine native raster and native vector data are commonly used to assess environmental quality. Most of these measurements can be calculated using either raster or vector data formats and processing methods. Raster processes are more commonly used because they can be significantly faster computationally than vector, but error is introduced in converting vector data to raster. This conversion error has been widely studied, but the impact on environmental decision making has not been addressed. We examined four GIS-based measurements of environmental quality in approximately 1000 watersheds in the state of Maryland and Washington, D.C. Each metric was calculated using vector and raster methods and estimated values were compared using a paired t-test, Spearman rank correlation and cluster analysis. Paired t-test results showed significant differences between methods for three of the four metrics. Spearman ranks were nearly identical between methods for all four metrics. Cluster analysis also reported nearly identical results between methods, with over 98% of watersheds assigned to the same group for three of the four methods. The paired t-test results are consistent with other studies that show credible differences in metrics that depend on whether estimation was done in a raster or vector format, but the Spearman rank correlations and the cluster analysis suggest that these quantitative differences would not influence environmental decisions.

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Citation:Wade, T. G., J. D. Wickham, M. S. Nash, A. C. Neale, K. H. Riitters, and K. B. Jones. A Comparison of Vector and Raster GIS Methods for Calculating Landscape Metrics Used in Environmental Assessments. PHOTOGRAMMETRIC ENGINEERING AND REMOTE SENSING 69(12):1399-1405, (2003).
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Contact: Chris Siebert - (702) 798-2234 or siebert.christopher@epa.gov
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Division: Environmental Sciences Division
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Branch: Landscape Ecology Branch
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Product Type: Journal
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Published: 11/24/2003
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Related Entries:
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Bullet Item Development of Landscape Indicators for Use in Regional Ecological Risk Assessments
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