Module 8: Isarithmic Mapping


The purpose of this lab was to investigate the PRISM Interpolation Method to develop an isarithmic map of average annual precipitation for Washington state. PRISM is a model that calculates climate-elevation relationships from point data for each grid cell in a digital elevation model (DEM). The data set for Washington state includes annual precipitation over a 30 year period (1981-2010). In this lab, I explored two methods for symbolizing this data in ArcGIS Pro.

The first symbolization method was using continuous tone symbology. Continuous tone symbology symbolizes a feature with differing shades between contours, where each point on the surface is shaded with a tone proportional to the value of the surface at that point. This results in a map where the shade of the colors vary and blend between contours, creating a smooth surface. A hillshade effect was applied to the map by using the Dynamic Range Adjustment (DRA) Hillshade Effect and editing the color and transparency of a color ramp.

The second symbolization method was hypsometric tinting, illustrated with contours in the map above. Hypsometric tinting is similar to continuous tone in that the data is symbolized with different shades between contours, however, unlike continuous tone, this is done by employing the shading in a step fashion. In other words, the area between two contour lines will have one specific tint or color. In order to symbolize the data this way, I had to use the Int(Spatial Analyst Tool) tool and Classify the data into 10 classes with Manual Intervals. In order to create and apply contour lines, I used the Contour List Spatial Analyst Tool and set the contour values to the same classes as the data. The same Hillshade Effect layer from the previous symbology was used in this map.

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