I'd have to say space maps, and open-ended ground maps.

By open-ended, I mean each team gets a lot of supplies at the main base, and the mapmaker basically says 'here you go, here are your tools to do battle, now fight it how you want to'.

I remember in GC the pleasure of many of the maps was that you could try out a skyhopper, grab the shuttle and ferry people around, or pirate it up and grab the sail barge with some friends.  It's like a world within a world, you know?  Adds depth instead of forcing players down one set path to winning a map.

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Proabably called like that because of the echo you can hear if you scream in the icey tunnels of it.

Or Yavin base was Delta, and Dantooine was Charlie and so on.