I think Higby was including Urban areas into the 'Indoors' percentage. I don't want to be misinterpreting him though so It'd be cool if he could give us an idea of the breakdown
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Even now in Planetside a large amount of the battles are within towers and bases, and a huge amount are within the SOI so 50% indoor is not that much different to the current % breakdown in the original game - add in Urban combat and I'd expect a huge amount of combat in Planetside would be indoors.