A COMPARISON OF EQUAL-AREA MAP PROJECTIONS FOR REGIONAL AND GLOBAL RASTER DATA

High resolution regional and global raster databases are currently being generated for a variety of environmental and scientific modeling applications. The projection of those data from geographic coordinates to a plane coordinate system is subject to significant variation and error based on the selected projection, the raster pixel size, and the specific latitude of the location being projected. While equal-area projections are designed to specifically preserve area, research shows that area preservation varies and selection of a projection for the resolution of the data is critical to developing accurate statistics of attributes such as land cover and elevation. In a comparison of four equal area projections, the Lambert azimuthal equal area, the Mollweide, the Goode homolosine, and the equal area cylindrical, results show that total areas of land cover vary with projection type and with raster resolution. While no single projection is best for all resolutions and at all latitudes, and any of the equal area projections tested are accurate with resolutions of eight kilometer pixels or smaller, the Mollweide appeared most accurate at larger pixel sizes. Analysis of the accuracy of raster projection was conducted by two methods. First, a set of twelve one by one degree squares placed at various latitudes were projected at several raster resolutions and compared to a projection of a vector representation of the same squares. Second, several different raster resolutions of land cover data for Asia were projected and the total areas of 21 land cover categories were tabulated and compared. The results indicate a variance in projection accuracy with latitude and among projection types.