How to make colliders for a map

I am new at unity. I was wandering how you make maps. Do you build the texture in a different program and then throw planes into the places where you need to collide? Or is there a program that will build one big collider for you. My main concern is not the texture right now but the collider building. Because I assume using millions of boxes and shapes for colliders would be way to much for processing and take AGES.

 

If this is in the wrong place I would be more then happy to. And sorry if this is obvious.

 

Hi!
What kind of maps? What kind of game? And is that 2D or 3D?
Maybe post some example images what you are aiming for..

 

Sorry. Forgot to add that. I am making a 3D RPG. I was wanting to make a city and a old town. And what I am looking for is a piece of software that allows you to have one object to import into unity that is the map. istead of having a thousand objects for collision.