It's a bit more complicated than that but not something I use anymore anyway - that's functionality I wrote about 12-14 years ago when I still did a lot of green laning and the commercial digital mapping options were pretty expensive and not all that good. Trailwise would have been pretty easy to support as well but I don't think that would have gone down very well with them.Wayfinder is dead Jon, company was dissolved in 2006, think it was all migrated onto Trailwise.
The free OS maps are good quality but don't include minor rights of way e.g. BOAT's