GPS help

I've been looking around at the GPS stuff, but I havnt been able to find some information.
1. Does it need to be high? I've seen some people's programs that make GPS triangulation spots near the world height limit. Is this necessary?
2. Range. I know that after a distance it won't be accurate, but up until that point, will it be 100% accurate? And if I place the computers farther apart, will it have more accuracy farther?
3. After the point where it is no longer accurate, is there a way to make sure it will not try to find it's place from that cluster? I want to have a bunch of clusters around my world so that it will be accurate where ever I need it to be.
Thanks

Rednet range is greater at sky limit, so you need the fewest GPS stations to cover a given area when they are as close to skylimit as possible.

At the default rednet ranges, rounding errors are not significant enough to cause issues at the edge of the range. I do not know whether the accuracy would be significantly affected at the edge of the maximum allowable range.

If maximum range is 100000 meters/blocks, and the modems of the GPS array are three blocks apart, then there shouldn't be any problem. Really, I don't think that you'll encounter a problem even beyond that. A standard GPS cross (+/-2,0/-1,+/-2) at the center of the world should provide valid fixes for anywhere else inside of a Minecraft world without problems arising from precision (though much beyond that and you will start to see problems, like if you put the GPS array on one side of the world and tried a fix from the other, the math might not work if it was a smaller than standard array).