We should re-evaluate the criteria and implementation of external layers, from a privacy and open source point of view.
There are some potential policies we could enact (some or all of the below) to move this feature closer to typical Wikimedia norms for privacy and open source (below is not how it currently works):
- All tiles must be rendered on Tool Labs.
- All tiles must be hosted on Tool Labs.
- All tiles must be generated with fully open source software.
- All completely external tiles must be proxied to protect privacy.
See https://en.wikivoyage.org/wiki/MediaWiki:Kartographer.js for how it currently works.