Assuming that there are no barriers legally (meaning national or regional communication laws that prevent this), I’d suggest that you split into two classes of wireless networks. By way of example, not all 802.1whatever channel ranges are legal in all countries, so you’ll have to do some homework.
One would be your “backbone”, operated with highly directional high-gain antennas, and with a router/access point at each registration area.
The registration AP/router areas should then have its transmission power cut down to just enough to keep them from interfering with adjacent ones. If you have a choice of channel ranges, put the backbone at one end of the channel spectrum, and alternate adjacent registration areas by at least a 2 channel separation and lock down all wireless clients and APs to prevent channel scanning.
Hope that helps,