We should probably only touch bg::point here, and make sure that its internal implementation does indeed use size_t only. For the other types: what they expose is up to their library writer, and our adaptation should just mimick that. The Point concept only wants traits::dimension<>::value to be a compile-time numeric constant, it doesn't define any constraint on its type. And the role of traits is to say what those libraries say, in a Boost.Geometry vocabulary. They should do just that.