I contacted them about using their tiles. I'm a bit unclear on the license (if there is one?), because it isn't displayed on their home page, but what I mentioned what I wanted to do with them (use them to make my own custom topos for free redistribution) he said that was OK:
"Because the underlying data is public domain I don't know if I could actually prevent someone from reassembling the tiles into a map, but I wouldn't want to even if I could. By all means feel free to do what you're describing."
When I asked about using the tiles in Viking, he basically said go ahead: "You guys should go ahead and use the tiles, and if bandwidth becomes a concern we can sort it out then."
projects / andy / viking.git / commit