Item spawners are meant to
reduce lag. When the limit is set to the amount of peices you'd have on the map anyway, the upper limit of the lag is the same as it would have been. And you can't spawn faster than the other team because the buttons have a reset time.
Nice map, but I was thinking more and more interesting cover, walls , trees, rocks, maybe a road with hedges, and definately partially-toppled standing stones

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The idea of people spawning outside of the obvious build area is one which needs to be discussed. On one hand, it means people have to have some kind of enterance to get in by, and may potentially make bunkers and satellite forts and things seem less remote and pointless, but on the other hand, it could piss people off if they have to run a long way just to get to their fort, and it may allow spawn raping.
I'm not keen on build walls, I like to see what the other team is doing. Even having a barrier reduces your freedom... surely building things too far away from your spawn is stupid anyway? Though the fort hills would definately have to have func_fortsites on them.
The peices should definately spawn on top of the hill, wherever the buttons are. I had some sort of arcane druidic markings or something in mind.