Module 6 - Isarithmic Mapping

This week's lab session will focus on isarithmic mapping. An isarithmic map is a specialized thematic map that employs color to depict smooth and continuous phenomena, such as elevation, temperature, or precipitation. Among the various types of maps, contour lines are particularly prevalent; they connect points of equal value to illustrate continuous elevation data.

The objective for this week is to create two isarithmic maps utilizing precipitation data for the State of Washington; a continuous tone map and a hypsometric tints map. The data utilized for this exercise has been prepared using the PRISM (Parameter-elevation Relationships on Independent Slopes Model) methodology.

The raster data representing annual precipitation (measured in inches) utilized in this map was sourced from the USDA Geospatial Gateway website. Data gathered from climate monitoring stations is transformed into grid points through various methodologies. Although these methodologies exhibit precision in flat terrain, they encounter increased complexity in mountainous areas. The Parameter-elevation Regressions on Independent Slopes Model (PRISM) has proven effective in modeling precipitation in sloped terrains. This technique combines point data with an elevation grid, such as Digital Elevation Models (DEM), to generate estimates of monthly, annual precipitation, and temperature. 

The initial map developed utilized continuous tone symbology. This representation method employs a gradient of colors that transition smoothly, rather than relying on distinct symbols or categories. In this approach, the colors on the map progress gradually from red to yellow, then to green, and ultimately to blue, creating a cohesive visual surface. The implementation of continuous tone symbology in these maps significantly improves the perception of continuity and fluidity in the presented data. Additionally, a hillshade effect was incorporated to further enhance the visual impact.

In the second map, we created a layout utilizing hypsometric tints, a hillshade effect, and contour lines. An isarithmic map featuring hypsometric tints employs contour lines and distinct colors to represent varying elevation levels. We employed ArcGIS Pro to convert the raster cell values into integers, facilitating the creation of hypsometric tints. Additionally, we utilized ArcGIS Pro to generate two new layers, a hillshade layer and a contour layer because elevation data is incorporated into the dataset. The hillshade layer was generated by utilizing the "Create Surface" function located within the Raster Analysis tab, while the contour layer was produced using the "Contour List" tool.

I found this week's laboratory session to be highly enjoyable. Upon completing the project, I took the initiative to download the PRISM data set for the year 2024 from https://prism.oregonstate.edu. I subsequently analyzed the yearly precipitation data for the continental United States, which further enriched my understanding of the creation and analysis of isarithmic maps.