I was reading the Special terrain rules.. I don't know where they are to post them here.. but there is a line about your characters getting +1 to defense if you can't play the terrain. But I didn't see exactly when that would happen.

If you win map roll and your opponent places a terrain? Is there only one special terrain allowed on the map or something? If that's the case, what happens with multiple shield cars and spider buggies?

One example is using the AI OP map on the side with all the different elevations (can't remember name). If your opponent wants to play a boxing ring they will not be able to since there isn't enough space all on the same elevation. I'm not sure about the vehicles.

Why it's always important to quote the effects, because there's your answer.

Special terrain can't be placed on multiple elevations or over other special terrains. Depending on map/expanded starting areas, you may not be able to place your terrain.

ok, so there's no limit to how many Special terrains are on the map other that the "one per force" at force construction? Just map placement issues.

Correct. And something like a shield car blowing up in a boxing ring.

This happened at states this weekend. I played against a boxing ring and won map roll. I picked Galador, which has elevated everywhere. Opponent couldn't place the boxing ring, so his characters got +1 ranged defense. I was playing Shredders, so I didn't mind.