Bit slow to come to this thread, but I see grahame was in naughty schoolboy mode when he translated Horfield as 'Maes Butain'...
I'm reminded of Adge Cutler's 'Bristol Song', with its line 'All the girls in Horfield, are quite respectable really'. This kind of thing was considered amusing in the 1970s.
Anyway, from my researches, and oddly enough all things considered, a better translation would be 'Tir Agored Budr', though FoSBR» would have it as 'Ffordd Gwnstabl'
Indeed, though the actual derivation of Hor isn't much better, as it meant 'dirty' and probably meant the area was always muddy.