Module 6: Isarithmic Mapping

 Module 6: Isarithmic Mapping

This weeks module the focus is on isarithmic mapping and how to present the data for the map reader to understand without much explanation. The isarithmic map is probably the most widely used thematic mapping method, and is also one of the oldest techniques, dating back to the 18th century, after the choropleth map. Isometric maps depict smooth, continuous phenomena, such as rainfall, barometric pressure, and topography or elevation. The most common form are contour lines.

The isarithmic map below is showing the annual precipitation over a 30-year period (1981-2010) by different techniques of continuous tone, hypsometric tinting, and contours lines. When making the map the first thing that needed to be done is creating the continuous tone. The continuous tone symbology refers to the representation of data values using a continuous range of colors or shades. The way this is implemented in the map is the symbology is of the average annual precipitation across the state of Washington for the years of 1981-2010. Also, on the continuous tone map we added in the hillshade effect to indicate the steep areas more effectively. This is important because we are able to show a 3-D view of the more mountainous areas compared to the flatter areas. Hypsometric tinting uses colors to represent elevation zones across the map. This was implemented on the map by using the data of the annual precipitation and changing the color ranges with equal to or less than 10 being red (lowest number) to greater than 180 (highest number). Contour lines are also a useful surface representation, because they allow you to simultaneously visualize flat and steep areas by the distance between contours, as well as and ridges and valleys by converging and diverging polylines. When using data it is important to understand where it is coming from and how it is collected. The way the precipitation data was derived and interpolated through PRISM, which is an analytical model that uses point data. Also, has an underlying grid of digital elevation model (DEM). This was used to generate a 30-year climate average through the years of 1981-2010 to get gridded estimates of monthly and yearly precipitation and temperature at 800 meters spacing. Lastly, on this map there is a paragraph to help the map reader understand how the information was collected and interpolated for the isarithmic map.