Cartography: Module 6

 Isarithmic Mapping

This week's exercise was hands-on application of isarithmic mapping, using Washington State's annual precipitation data. Isarithmic mapping is a technique used to illustrate smoothly varying phenomena across a geographical area through the use of isolines- lines that connect points of equal value. The term "isarithmic" is often used interchangeably with "contour mapping," with specific types of isolines named according to the type of data they represent (e.g., isobars for pressure, isotherms for temperature, and contour lines for elevation).

This dataset was derived with point data and interpolated using PRISM (Parameter-elevation Regressions on Independent Slopes Model). PRISM is is an analytical tool that leverages point-specific data and a foundational grid, such as a digital elevation model (DEM) or a 30-year climatological average (for instance, from 1981 to 2010), to create grid-based estimates of monthly and annual precipitation and temperature, among other climate variables. This model is particularly effective in mountainous areas due to its inclusion of a conceptual framework that considers the spatial distribution and scale of orographic effects. Temperature grids annually are calculated by averaging monthly grids, while precipitation totals are obtained via summation.

Hypsometric tinting was used to create a 3D surface by symbolizing different colors for elevation contours. This map compares the elevating model of Washington state with annual precipitation data, because the two are intrinsically correlated. Precipitation runoff makes its way downhill, so lowlands surrounding high elevation will be substantially wetter. This technique not only adds an aesthetic dimension but also provides useful information at a glance about the terrain.