GIS 5007 - Isarithmic Mapping

 Isarithmic mapping is another type of thematic mapping that results in continuous phenomena of a geographic area being displayed using various symbology methods. The continuous phenomena typically displayed can include precipitation, elevation or topography. As it is difficult to record values for every single point across any given area, isarithmic mapping utilizes data from control points (true point data or conceptual point data) and interpolates the data using one of many interpolation methods to calculate the various intermediate points, producing a continuous surface. The interpolated data can then be symbolized to present as smooth surface using continuous tone or a stepped surface using hypsometric tinting. Contours can also be created and displayed as a stand alone feature or in conjunction with hypsometric tinting. Using the contours along with hypsometric tinting is recommended, however, because it helps the map reader obtain a better understanding of the data being displayed. 

For this week's lab assignment we were tasked with creating a map of annual precipitation in the state of Washington. This assignment would allow students to produce their very own isarithmic map and utilize some of the methods highlighted in the lectures. 

Map of Annual Precipitation - Washington State, USA. 

To create this map precipitation data ranging a 30 year period (1981-2010), digital elevation model (DEM), and point data were used in an analytical model called PRISM (Parameter-elevation Relationships on Independent Slopes Model). The model produced monthly models that were then averaged and summed to provide an annual average. The annual precipitation raster dataset was then utilized to produce a dataset containing values converted to integers by truncation, which was used in conjunction with a generated hillshade dataset to display the raster data split into 10 classes with 10, 20 and 40 inch intervals. Contours were also created to further highlight the classes at previously mentioned intervals. This map above symbolizes the data using hypsometric tinting. However, we were also tasked with symbolizing the data using continuous tone, although a map product was not required.