The only groups to have allotted camp sizes are registered theme camps and villages. The spaces taken by them will be clearly marked when the map for this year is released.
Only take as much space as you need for your camps- tents/ RV's/ hexayurts, shade structure, parked vehicles etc. "Landgrabbing" (taking more space than you need) is considered rude in BRC. If you want some space to spread out, camp on the back streets where there is almost always extra room. This satellite view
will give you a good look at how tight it can get in some places and how open it gets towards the back (further from the Man)