Let’s say two friends each want to buy “an acre of land.” Mr. P’s acre is on a flat plain; Mr. M’s is on a mountainside.
Are both plots defined by surface area dimensions – that is, paced off on the ground regardless of its inclination? (Thus Mr. M’s plot will have the same surface area as Mr. P’s.)
Or are they defined by “footprint” dimensions? (Thus Mr. M’s plot will contain more surface area than Mr. P’s.)
An acre would be surveyed to be an acre in map view, so a hilly acre has more surface area than a flat acre.
Bah, Ringo beat me to it. I was even going to throw in the IAASurveyor too.
This doesn’t have anything to do with fonts or typefaces. 
Did you mean cartography?
Akk! Sorry, Audrey, you are right.
Of course I meant TOPOGRAPHY.
If a mod would change it I’d appreciate it (though I think I got my answer anyhow).