Add an option "Switch to similar map scale when changing maps"

[LaurentG]

There is an issue when switching from a raster map (eg. in OTRK or mbtiles format) to Mapsforge vector map : in mapsforge map, zoom level 15 corresponds +/- to zoom level 16 in raster, 14 in mapsforge to 15 in raster, etc....

So it would be great to be able to do NOT switch to the same zoom level, but rather to the zoom level which gives the same coverage.



See details and beginning of explanation in this post : https://www.oruxmaps.com/foro/viewtopic.php?f=5&t=5252">https://www.oruxmaps.com/foro/viewtopic.php?f=5&t=5252