EFFECTS OF GEOGRAPHIC INFORMATION-SYSTEM VECTOR-RASTER-VECTOR DATA CONVERSION ON LANDSCAPE INDEXES

The effects of geographic information system (GIS) data conversion on several polygon-and landscape-level indices were evaluated by using a GIS vegetation coverage from eastern Oregon, U.S.A. A vector-raster-ve ctor conversion process was used to examine changes in GIS data. This process is widely used for data input (digital scanning of vector maps ) and somewhat less widely used fur data conversion (output of GIS dat a to specific formats). Most measures were sensitive to the grid cell size used in the conversion process. At the polygon level, using the c onversion process with grid cell sizes of 3.05, 6.10, and 10 m produce d relatively small changes to the original polygons in terms of In(pol ygon area), In(polygon perimeter), and 1/(fractal dimension). When gri d cell size increased to 20 and 30 m, however, polygons were significa ntly different (p < 0.05) according to these polygon-level indices. At the landscape level, the number of polygons, polygon size coefficient of variation (CV), and edge density increased, while mean polygon siz e and an interspersion and juxtaposition index (IJI) decreased. The yo ungest and oldest age-class polygons followed the trends of overall la ndscape only in terms of number of polygons, mean polygon size, CV, an d IJI. One major side effect of the conversion process was that many s mall polygons were produced in and around narrow areas of the original polygons. An alleviation process (referred to as the dissolving proce ss) was used to dissolve the boundaries between similarly attributed p olygons. When we used the dissolving process, the rate of change for l andscape-level indices slowed; although the number of polygons and CV still increased with larger grid cell sizes, the increase was less tha n when the dissolving process was not used. Mean polygon size, edge de nsity, and fractal dimension decreased after use of the dissolving pro cess. Trends for the youngest and oldest age-class polygons were simil ar to those for the total landscape, except that IJI was greater for t hese age-classes than for the total landscape.