GIS, spatial statistical graphics, and forest health
This paper discusses the use of a geographic information system (GIS), Arcview 2.1, linked with a dynamic graphics program, XGobi, in the statistical analysis of spatial data. The link allows multivariate data, collected at geographic locations and stored in Arcview, to be passed into XGobi and analyzed dynamically. The connection between the points in XGobi and the spatial locations from which they were collected is maintained so that points in either Arcview or XGobi can be brushed and the corresponding points in the other application identified immediately. Spatial cumulative distribution functions (SCDFs), spatially lagged scatter plots and variogram-cloud plots can be displayed in XGobi using the link. In each type of plot, the connection to the spatial sampling location is maintained and user interaction can take place in either application. The link is used to predict and analyze SCDFs of forest crown health in the northeastern United States. The SCDFs are predicted from field data collected as part of the U.S. Environmental Protection Agency's (USEPA) Environmental Monitoring and Assessment Program (EMAP). The field data are augmented with concomitant geographic information, including Landsat Thematic Mapper images, digital elevation models, and population information, which are used to improve the SCDF prediction.