This is interesting info. What I would like to do is to replace some of the highest resolution tiles with scanned images from Ordnance Survey maps showing contours, footpaths etc. I don't know how practical this is, but in order to do it I need some way of working out the corner co-ordinates of a tile. If I am able to create my own tiles then I would want a way to tell APRSISCE never to replace those tiles, without interfering with its ability to download or update the OSM tiles.When I get to the task about adopting UI-View-formatted and pinned map displays, I can support a "priority" setting on those. If the priority is set higher than whatever I set for the default OSM tiles, then when the client needs to display information in that area at a particular zoom range, it will choose to use that map instead of the OSM tiles. That way you won't have to land exactly on an OSM zoom level or tile boundary. Of course, it will only use a single tile for any 256x256 pixel area, but once you zoom in close enough, the manually-added tile will probably meet that requirement.
Lynn (D) - KJ4ERJ - Added to the ToDo list