Utilizing contours formed by connecting points of equal values, isarithmic
maps are useful for illustrating continuous data such as elevation and
topography, barometric pressure, and precipitation. This module’s exercise
focused on the average annual precipitation of Washington State and involved
the completion of two isarithmic maps, one symbolized with the continuous tone method and
the other symbolized with hypsometric tints.
As seen in the first map, the continuous tone technique is a proportionate
tonal representation of each surface point’s value. Because this results in a
gradual change in color with changes in quantity, distinguishing between
quantities can be difficult when trying to relate the values in the legend with
distinct locations on the map. That is why I chose to provide contour lines on
this type of map. Contour lines provide “break points” in precipitation amounts
relative to the legend.
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| Map 1: Continuous Tone Isarithmic Map Average Annual Precipitation: Washington State (1981 - 2010) |
Hypsometric tints were used for the second map. Hypsometric tinting has
discrete breaks between ranges of values. The abrupt changes of color enable a
viewer to more easily distinguish the differences between values. Unlike
continuous tone maps, maps with hypsometric tinting can be used easily without
contour lines. Creating the map from the data involved converting the raster
data to integers and then manually forming classes to symbolize.
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| Map 2: Hypsometric Tints Isarithmic Map Average Annual Precipitation: Washington State (1981 - 2010) |
For both of these precipitation maps I selected a vertical-format legend
for a couple of reasons. The first reason is that precipitation is a
"vertical" measurement of volume (imagine a rain gauge) with values
increasing toward the top. The other reason is that greater
precipitation generally is associated with higher elevations. A vertical format legend
echoes those relationships (lower/dryer, higher/wetter). Deciding which legend format
to use was definitely the easier part of implementing it. Trying to remember
where and how to change the symbology and format ended up being a bit time-consuming
due to minimal experience. I’m glad to
say that that is improving with every lab exercise. With their use of hillshading effect and vibrant color ramps,
these maps rank among my favorites to create so far.
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