How do I measure the circumference of a circle without the given radius/diameter?

Question

How do I measure the actual distance between Grande Prairie and Medicine Hat? Map Scale: 1:18,300,000

Answer 1

measure the distance on the map, in cm.

Then multiply that by the map scale (18,300,000) to get the real-world distance, in cm.

Divide that by 100,000 to get the distance in km.