ATTRIBUTION

What to show on screen whenever terrain (hillshade or contours) is actively rendering.

Deliberately generic rather than an enumerated per-source credit: Mapterhorn's data is a mosaic of 100+ regional datasets under a mix of licenses (CC-BY-4.0, CC0, national open-data licenses, US public domain — see mapterhorn.com/attribution/, fetched and confirmed during this feature's research, not assumed), with no single blanket license covering all of it. Computing which specific sources a given downloaded region actually draws from would be the fully-correct answer, but is real additional engineering; this generic credit plus a link to Mapterhorn's own attribution page is the honest, low-risk baseline both flavors should ship with now, upgradeable to a per-region source list later without changing the UI shape that reads it.