Information:
The PvP area accounts for approximately 10% of the map. When deciding where to put the divider, we chose a nice round percentage and constructed the divider in such a way that the area of the (PvP) segment accounted for 10% of the total area. This was slightly changed so that the divider was suitably epic with a nice warning message, but you'll be able to see that all for yourselves soon!
Hopefully this is large enough that there is enough room to have multiple fights, with a bit of running, a bit of hiding etc. But not so large that the PvP area is totally safe.
A nice picture showing the maths behind segments