For reference, this is the size of the town for each game in 16x16 acres:
Pink: Wild World
Light Blue: New Leaf
Orange: City Folk
Green: GCN
I think that graphic is a bit misleading though, since 20 acres (NL) would be 5x4...so it wouldn't be both wider and longer than the 4x4 WW map, just one or the other. Same deal with CF (5x5) vs. GameCube (6x5).