How large is Greenland, really? Your map may be deceiving you : NPR

President Trump floats the idea again annexation of Greenlanda semi-autonomous Arctic island that is Danish territory.

Greenland's location between North America and Russia gives it strategic value to the United States, which has already there is a military base there. “We absolutely need Greenland,” Trump said Sunday. “We need it for defense.”

If all this talk makes you want to look at Greenland on a map, you may notice its size. Greenland is the largest island in the world, occupying more than 836,000 square miles.

But is Greenland really as big as it appears on the map? Turns out it depends on the card.

Although globes provide a fairly accurate picture of the geography of the world, things get much more complicated when you try to depict a sphere on a two-dimensional surface. The shapes and sizes of land masses may become distorted, and distances and directions may become uncertain. There are many different types of world mapsand each has its own strengths and weaknesses.

One of the most common types of cards is called Mercator projectionnamed after the 16th-century Flemish cartographer who invented it. This is the one you may have seen in an atlas as a child, and version of this used in online mapping tools such as Google Maps.

The Mercator map takes the Earth's latitude and longitude (parallels and meridians), which go around a spherical globe, and turns them into straight lines.

This allowed sailors to plot a course between any two points in a straight line, but it also caused the map to distort as they moved away from the equator. For example, Greenland looks about the same size like the African continent on Mercator's map, although Africa is about 14 times larger.

“Mathematically [the parallels and meridians] move apart, stretch out to varying degrees and magnitudes from the equator to the poles, so you end up with a sort of exaggerated effect, if you will, in the upper latitudes where the landmasses appear huge,” said Fritz Kessler, a Penn State geography professor and expert on map projection.

There have been organized efforts to move away from the Mercator projection and use alternatives that offer a more accurate representation of the relative size of the earth. Robinson projectionwhich attempts to better balance the size and shape of the land, sought to solve the “Greenland problem”. And last year African Union supported for attempting to replace Mercator with the Equal Earth map, which better conveys the scale of the continent.

But according to Kessler, which of the many map projections you choose at any given time really depends on what you're using the map for.

“Will it be used to measure distances or directions? Angles? Areas? Show the distribution of thematic data, well, population?” – he said. “There are hundreds of forecasts that can be used, and the fact that we're only focusing on a very narrow subset I think is another problem that needs to be addressed.”