Distances on a world map: the classic geodetic blunder

This week a classic map projection problem reappeared in my Twitter timeline (thanks to @petzlux). In 2003, the Economist featured an article about North Korea’s missiles, including a map showing their purported range:

The original map by The Economist, 2003.

The original map by The Economist, 2003.

Of course, it didn’t take long for the more map-savvy readers of the publication to realise that circles on a map aren’t circles in real life, especially on a Mercator projection. Two weeks later (which seems like a long time by today’s standards) the Economist posted a correction, updating the map. And sure enough, with an alleged range of up to 15,000 km, now practically the whole world was within reach of the missiles:

The corrected map. In real life, those blue and red lines are actual circles spanning the earth's surface.

The corrected map. In real life, those blue and red lines are actual circles spanning the earth’s surface. (credit: The Economist, 2003)

This is a well-known example of how map projections can play tricks on your perception of reality, accidentally or purposefully. If you’re interested, the phenomenon of geodesic buffering is explained quite well in this Esri blog.

It is also, for example, why airliners don’t fly in straight lines across the Atlantic – they do, of course, but the map makes straight lines look curved and vice-versa. But it keeps confusing people.

 

 

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6 thoughts on “Distances on a world map: the classic geodetic blunder

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