Ballistic Blunders: a Geodetic Cautionary Tale

In light of the recent noises coming out of North Korea, I wasn’t too surprised to see an article about their missile ranges.  However, I was dismayed by the following infographic:

badMissiles


No, I’m not upset at the range of the missiles, I’m upset with how the cartographer drew them.  What you see there is a Euclidean distance range, which only takes into account the Cartesian coordinates.   The map should really look something like this:

Notice the difference?
Notice how the first map vastly underestimates the portion of the globe the missiles could potentially reach.  Why is there such a big difference?  This is a result of how the globe is projected onto the flat map sheet.  Trying to fit a sphere onto a flat surface inevitably introduces distortions of one sort or another.  Because of this, the scale actually varies across the map.  In this case, the scale gets larger with increasing latitude.  The real problem arises when a mapmaker performs a simple Euclidean buffer, which is based off of map scale.
While this works well enough for local analyses, trying to do the same thing over a larger area will produce incorrect results.  When working at continental or global scales, you need to instead use a geodetic distance, which accounts for the true distance over the surface of the Earth.  This looks really strange and wrong, but it makes sense when you realize the distortions introduced by projecting your globe will also apply to your distances.
This is a great reminder of how you have to keep distortions in mind when reading, analyzing, or creating maps.  It’s easy to just take the map at face value, but your conclusions are going to be incorrect if you use the map incorrectly.  This is especially true when working with a map that covers large areas.  Unfortunately, I see this kind of mistake pretty frequently.  In fact, I recall seeing another incorrect map of the very same subject a few years ago, and someone wrote the same criticism.  If anyone knows the link to that other map/criticism, please let me know in the comments.  It’s too bad some mappers seem to not have learned their lesssons, but we should all take heed and make sure to make our maps carefully and use them wisely.
 

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Author: jcguarneri

Mapmaker, bicycle advocate, fisherman, naturalist. Follow me on Twitter @jayguarneri.

2 thoughts on “Ballistic Blunders: a Geodetic Cautionary Tale”

    1. Thanks for sharing that article, Reinier. I came to GIS/Geography from an Environmental Science background, so I love learning more about the history of the field and the technology, and how they interact.

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