I am working on better rules for the mkgmap default style regarding unpaved roads.
Up to now I thought that a highway=bridleway is a way with soft surface because in my home area
I only see those. My understanding is that a horse doesn’t like to go on a paved surface. So I wonder
why so many ways in the UK have the combination highway=bridleway and surface=paved.
There are probably a few reasons why you’re seeing a discrepancy:
One is the preference in the UK for footway/bridleway/cycleway instead of “path” (with a complicated series of qualifiers).
Another is a highway=bridleway in the UK will likely be for mixed traffic (foot, horses, bicycles) rather than just horses as may be the case in more “regulated” countries.
Still another is that some “highway=bridleway” may actually be a mistagging for “designation=public_bridleway; highway=something else” (or date from before when “designation” tagging became commonplace.
I had a brief look locally http://overpass-turbo.eu/s/lOY and the ones I see do look fairly plausible. For example, https://www.openstreetmap.org/way/97044835/history definitely qualifies as a highway=bridleway - it’s a former miner’s track now optimised for horse traffic, and carries a fair amound of that, but is paved to deal when the river decides to flood. It’s not wide enough for 4 wheeled traffic.