An urbs is a city, an oppidum is a town.
It is quite common to use urbs to refer specifically to Rome, and the linked dictionary entry even says that oppidum is used for other cities than Rome.
You could say that urbs is a capital and oppidum is a regular city.
There are a number of ways to phrase and see it, but the crux is: urbs is bigger (in size or ...
I would suggest simply the word forma.
It means all kinds of things related to shape, size, form, and such.
The linked entry in L&S (I.B.2) gives "outline, plan, design (of an architect, etc.)".
Formatting is the design of a page much like how that part of the dictionary entry describes the design of a house.
I found no attestations related to ...