I walk the rights of way either with the ramblers or explore them myself. I record them with a Garmin Oregon 450. I check the route against council signs and the Definitive map hosted by most county councils, and i then add them to OSM. If the path is already on the map and matches my survey fine. If it is a slightly off line and there are several traces I go with the best average. There are quite a lot of armchair mappers which is OK if the paths are accurate, but some are traced from out of copyright map backgrounds, You can use your usual check on these and most field paths are clear on Bing although the line of cross field paths can change a little from year to year as the farm worker sprays (with weed killer) to comply with the law and may go a little off line with he his quad bike. I plot these as dead straight between marker posts. In my opinion it's much better to have a nice walk and survey what is on the ground. If the farmer does not reinstate the path and there is a good alternative along the field edge I do map that as well, if that is the route i take, but I don't use the designation tag. tag for this alternative. happy mapping.