GIS 5007 Module 6: Isarithmic Mapping

    Module 6 of Computer Cartography focused on isarithmic mapping and using PRISM (Parameter-elevation Regressions on Independent Slopes Model) derived data to showcase the annual precipitation of Washington state, USA over a ~30 year period (1981-2010). Originally created by the PRISM Group at Oregon State University, the PRISM system has proved to be a leading system in producing quality precipitation maps. A climate-elevation regression function is calculated in PRISM with consideration of climate variables that may influence the data, such as proximity to coast, atmospheric layer, topography of region, and more. As precipitation tends to increase with elevation, elevation is an included variable in PRISM using a digital elevation model (DEM) and each DEM grid cell has its own climate-elevation regression function calculated within.

Annual Precipitation of Washington, USA from 1981-2010

    The above isarithmic map depicts the annual precipitation of Washington state, USA over a ~30 year period (1981-2010) using the PRISM data described above. The red areas indicate less annual precipitation in inches of rainfall, and as the symbology continues towards blue, the more annual precipitation in inches an area has. Note that the higher elevated areas have more precipitation. To make this map, we started by showing the Annual Precipitation (in) raster data in a continuous tone format. To do this, we ensured that the data was in an appropriate Symbology- in this case, of course, choosing the Precipitation color scheme. We created a copy of this data to create a relief on the map – within that copy, we utilized the Hillshade function to create a relief in the map and adjusted this function using Dynamic Range Adjustment (DRA) to better indicate elevation. We added hypsometric tint using the Int (Spatial Analyst Tool) to enhance shading between the contour lines that we added lastly.