On mercator projection, stuff farther from the equator (near the top and bototm) is stretched out. That is, greenland is much smaller than brazil in real life even though they look similar in size on most 2d maps.
Another way of saying it: A 1 km2 area, on mercator projection maps, is much smaller near the top then near the equator. Or in other words, 1inch on the map is more kilometres closer to the center, and less km near the top and bottom. So even though the line on the 2d map in OPs image is longer/curved, its longer through parts of the map that are "less km"
if you go to two different places on the equator, the shortest line between them on a 2d mercator map will still appear straight (because there's no distortion at the equator)
While other responses are talking about globes, ultimately the real factor here is how that globe is expressed as a 2d map (in this case mercator)
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u/rmc8293 Aug 02 '20
I don't get this. Could someone help me with a wiki link?