Isarithmic mapping is one of the most popular methods of displaying
data that is smooth and continuous. The contour map is the most common style of isarithmic map and is widely used to
present data on topography, elevation, and rainfall. This week’s lab required that I make two isarithmic
maps depicting average annual rainfall in the state of Washington. One map would be symbolized with a continuous
tone while the other would employ a hypsometric tint design. Both maps would also use a hillshade effect
to enhance the data contours.
The data for this lab was gathered from the U.S. Dept. of Agriculture
through their Geospatial Gateway website but was originally created by researchers
at Oregon State University by using an interpolation method called PRISM
(Parameter-elevation Relationships on Independent Slopes Model).
Map 1 was titled “Continuous Tone” and was symbolized with the
Precipitation color ramp provided by ArcMap.
I added a vertical legend and stretched it so the numbers and colors
were easier to read. I also added some
key cities to the map to serve as a reference for viewers unfamiliar with
Washington geography.
Map 2 was titled “Hypsometric Tints” and symbolized in the same manner
as Map 1. For Map 2 I utilized a
horizontal legend and manually adjusted the 10 classification values that were
called for. To make the classes easier
to display in the legend we used a tool from the Spatial Analyst extension that
rounded fractional numbers to whole numbers.
Another difference between the two maps was that for the hypsometric map
I added contours at specified intervals related to the amount of average annual
rainfall. To add a bit of craftsmanship
and refine the map I decided to make the precipitation layer 20% transparent and
placed the contour layer below. This
arrangement offered the benefit of the contours layer without giving the map a
cluttered appearance. I felt this really
improved the readability of the map when combined with the hillshade effect.
I hope the audience will come to appreciate how effective and powerful
isarithmic maps can be in understanding our world.
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