The association says there are thousands of miles of tracks across the nation that have not been shown as having public right of way. John Trevelyan, the association's deputy director, said the OS decision was a significant victory for people who want to walk in the countryside.
"The first map is an experiment but I'm sure it will be worth repeating on other maps covering all of England and Wales. We will certainly be recommending this map to members. It is the most important mapping breakthrough for us for many years," he said.
OS has chosen a diamond notation in the same magenta as the public rights of way symbols to indicate "other routes with public access" in the Landranger Map 124 covering Dolgellau and the surrounding area. The paths would be listed as having public rights of way on county council maps, but searching them out is impractical for most walkers. Users have until December to let the OS know their views on the new map.
Mr Trevelyan said the tracks often formed important links with other recognised footpaths and therefore opened up many new routes for ramblers. He did not envisage many difficulties with local landowners because the tracks are in existence and right of way is not new. Existing rights are merely being publicised.
However, the possibility that owners of four-wheel drive vehicles might use the information to pursue their sport did give cause for concern both to ramblers and landowners. Mr Trevelyan said: "It might create conflict and we will have to see what happens."
In the mountains north of Barmouth, the Pont-Scethin bridge is a popular landmark for local walkers. The stone bridge is on the old stagecoach route between Harlech and London. But in the past it was not shown as having public access.
For locals, not being listed presented no problem. But this part of Wales is a popular tourist destination and many visitors will have been put off using the walk because of uncertainty over rights of way. That has now been cleared with the new map.
Geoff Elliott, a member of the local Ramblers Association committee, said: "It is important that areas of doubt like this should be cleared up for the benefit of everyone. While Pont-Scethin bridge is well known, the map also reveals tracks that even many locals would have been unaware were open to the public. Although this is a pilot to see how it is received, the revealing of previously hidden routes must be welcomed by all ramblers."
Another move applauded by the Ramblers Association is the return to the map of information on publicly-owned Forest Enterprise woodland where walkers can roam. The OS dropped this information from all Landranger maps in the mid-1980s because of the Government's policy of selling off the woodlands.
Mr Trevelyan said: "I think these changes partly reflect us nagging but also OS has become more customer-orientated. They are looking to supply a service rather than produce maps, and they perceive there is a need for this."