Module 6: Isarithmic Mapping

    For this week's lab, I mapped annual precipitation for Washington state using ArcGIS Pro. The precipitation data was generated by the Parameter-elevation Relationships on Independent Slopes Model or PRISM. PRISM uses an analytical model which incorporates an elevation layer (DEM) and the 30-year average precipitation records from weather stations to create the gridded estimates for monthly and annual precipitation (and other climate metrics). More specifically, the weather stations are assigned a weight based on the similarity of that station to the grid cell being interpolated. The weighting is based on parameters such as location, elevation, and more. Once weighted, a climate-elevation regression is used to determine the estimated precipitation for that grid cell. The inclusion of elevation data increases the accuracy of the interpolated metrics especially for more rugged terrain (i.e. western US).

    We also explored different ways to symbolize the precipitation data such as continuous tone and hypsometric tinting. Continuous tone offers a more precise means of mapping the precipitation data since the data remains unclassed, but this method can make interpreting the map more difficult for the user. In the end, I decided to use hypsometric tinting due to the increased readability of the map. Hypsometric tinting classes the data and symbolizes the data between the contour lines for the classes. In my map, the classes ranged from 10-40 inches of precipitation. This classification allows the map user to easily identify which class an area on the map belongs to based on the color of that area. The contour lines also help to differentiate the classes on the map more clearly.

Don't forget to check out next week's post on Neo Cartography!