I don't really think there is a set size or pattern. Though there may be for X-ball. However, You may want to chack out the NPPL site or any of the other mainstream Prop-Paintball sites and browse their rules sections.
Those are just terms borrowed from football. The 50 is the 'middle' of the field, and the other 'yard lines' designate 1/4, 1/3 or whatever of the field. I have yet to see a 100 yard airball field.. but I don't think there is a rule against it.