Let's specify this question[a] a bit:
I'm not interested in how big the continents or whole world are supposed to be, but rather in an approximation (or measurements) how big all the zones[b] combined are on all the continents together.
That is, map size in km² / mi² / real world comparison when comparing the zone sizes with the avatars size and how long it takes one to run through.
I would appreciate answers that are backed up by some research. Educated guesses are welcome too, but please try to motivate how you arrived at your guesses. :-) Thanks!
[b]: I never played that much. Are they called "zones"? If not, feel free to edit.