The maps are Heightfield data, with a texture, but it also has a materialmap, which defines the physics and sound of each peice of terrain.

But also, each control point, spawn point and vehicle spawn point are defined by script files, and in these script files there are many possible combinations. For instance, people found that creatine a vehicle with a spwn point attached means you don't nee to have flags or control points, and if this vehicle is the only spawn point, when it is destryed, that team spawning from the vehicle loses, thus creating an objective mode, the opposing team needs to destroy the vehicle, instead of capturing flags.

Then, you can take that further, and turn a building model into a vehicle, but take away the vehicles entry points (so the vehicle cannot be "used") making the building destroyable, and then with the afformentioned info, make it so you need to destroy the building to win.

as the MOD community is still young, we are still find new and more ways to manipulate this stuff, making it a lot of fun, you can also manipulate some of the game files, like weapons kits and vehicles from within the mapfile, makings even more tsuff to play with... its quite dynamic. Its just ashame there is no dynamic lighting

...maybe in BF:V...

If somehow the 1st person ground combat of DoD, the foliage and nature graphics of Ghost Recon, and the vehicles and map sizes of BF1942 could be merged into one uber-game, I'd be in heaven.