Ah a classic! The travelling salesperson problem. I wouldn't recommend QV as the best environment to solve it, but it can be useful as a tool to play around with the route.
As for distance between longtitude and latitude, most accurate is if you look up actual traveling distances/times, as this can deviate a lot from 'fly-distance'. But if you want to estimate distance when actual distance is not known, you can take a look at the Haversine formula.'You typically create a matrix containing all distances between all points.
Visiting the nearest neighbour on every visit is easy to implement, but is known to sometimes give efficient and sometimes very inefficient routes.
gl Jeroen
