As the crow flies

"As the crow flies" or "in a beeline" is an idiom for the shortest path between two points (on a map, disregarding the vagaries of intervening terrain); the geodesic distance.

An example is the great-circle distance between the cities of Key West and Pensacola, at either end of the U.S. state of Florida, where the direct point-to-point aerial transit path (as the bird flies) is 524 mi (843 km), but the shortest route by road is about 792 mi (1,275 km).

The phrases are attested in print as early as 1758.

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