Posted in the Junior thread but think it belongs here.
See this Highland line business. How no just do it by postcode and allow DD to have the choice to go Highland if they want (except DD6 who are always Lowland). Something like:
Lowland League
DG, TD, ML, KA, G, EH, KY, FK, PA, DD*, PH1-PH14
Highland League
ZE, KW, IV, PH, AB, HS, PH15-PH50
*All DD postcodes are eligible for Lowland League. All DD with the exception of DD6 are also eligible for membership of the Highland League system should a membership application be accepted.