For the purposes of my problem, we can forget about times. Let's assume that each sales rep only has one call per day. My problem is merely about the best geographical assignment.

Cost of travel is tricky - althought nowhere near as tricky as in your situation. Most reps will hopefully not be travelling that far (if I can get this algorithm right!!!) and all will be travelling by car: hence, no plane scheduling problems, and no allowing for travelling by planes, trains or automobiles as appropriate.

Hence, I've boiled the scoring mechanism down to simply one of distance. (I'd love a way of estimating time to travel, because of course 50 miles up a motorway is slightly different to 50 miles straight across a town centre. However, whilst I'd love any help on this (I'm in the UK, if you're going to suggest any route-finding services), this is definitely out-of-scope for my original problem.)

Thanks again,
SmugX.