What does "as the crow flies" mean — and why is it funny?

informal

Meaning

In a straight line; the most direct distance between two places, ignoring roads and bends.

Where it comes from

An English phrase from the 1700s, from the belief that a crow flies straight to its destination rather than wandering about.

Why it is funny

The mild humor is trusting a crow with your measurements. Roads twist and rivers bend, so the phrase quietly appoints a passing bird as the official surveyor of the shortest possible route.

Used in a sentence

"It's only two miles as the crow flies, but six miles by road."