Isarithmic Mapping and To Contour or Not To Contour.

Good day readers,
      The subject of this post is this weeks Cartography assignment dedicated to Isarithmic mapping. That is maps that depict smooth, continuous phenomena such as rainfall or temperature across an area. The most common of these is a contour map. Before we get any further lets look briefly at the assignment and some of the objects I worked toward along the way. This assignment was based of the school provided data of precipitation over a 30 year cycle for Washington. It was mapped entirely in ArcMAP. Some objectives are as follows:

• Define an Isarithmic Map, review different kinds of isarithmic maps
• Identify appropriate data types for Isarithmic mapping
• Recall different interpolation methods (Triangulation, kriging, Inverse Distance Weighted, PRISM)
• Recognize the different symbolization methods
• Describe the basics of and create contour lines
• Work with continuous raster data
• Implement continuous tone symbology
• Implement hypsometric symbology
• Employ hill-shade relief 

The biggest difference between the two final products below is the method of symbolization. The two methods portrayed are that of Hypsometric Tinting (first / preferred map) and a Continuous Tone map. Lets look at the definition followed by the map employing the technique.

Hypsometric Tint: These are shaded or color scaled areas between contour lines that enhance your ability to visualize a 3-D surface because we can associate the lighter colors with lower values and darker colors with higher values. 

As you can see this map is classed, showing specific value ranges for each specific color. It is also contoured to given further definition to the changes in value. Interpolation and the PRISM method are both introduced to help interpret the map. Given that we want to know where the areas of higher and lower rainfall occur, and both are equally important a diverging color scheme is employed. Not the dark orange for lowest values, and dark blue for highest.  Hill shading is also employed, essentially breaking out the natural terrain be adding shadow to the terrain features.

Continuous Tones: This style differs from the above by showing a smooth transition for all values, where each point is shaded with a color tone proportional to the data value at that point. 

This map shows a steady changing in color tone from the lowest to highest values. You can see that this causes some washing our of areas with very steady values such as the eastern portion of the state where values are lowest. you lose a sense of the depressions that is more clear in the hypsometric tint map. Hill shading is also employed. As this was not my preferred map I chose not to employ contour lines on it. given the washed out nature of some of the colored areas, when employing contours they appeared more haphazard given the values they represented.

This has been a look at Isarithmic maps. Thank you for your time.