Yes, the minefields are an abstraction exactly as Nic described (I created one for my El Guettar map in TOW2 Africa). But, if it's any consolation -- in the time frame represented by the battles in this game, there wouldn't have been time to really clear minefields, so attacking units would most likely blunder into them or, once the mines were detected, try to skirt them. Any well-planned minefield is always covered by lots of MGs, mortars and maybe even artillery, so they serve to channel the attacker into other areas.