It's a cultural thing...

WE think in terms of bird's eye view, down from above, etc naturally. It is very difficult for us to conceive how someone who never flew would have a gap hard to leap to conceive of a look down from straight up...

Most of the AE maps I've run across are elevated 3D horizontal view, as Hermione's excellent example shows.

The Battle of Qadesh (Kadesh) Relief panel in the Ramesseum is another example of a 3D elevated view map.

Most of our cartography came after the invention of aerial photos btw, with the biggest jump being satellite mapping, neither of which the AE had...

Jammer