Hi Steve, I hope you can help me out here. I've implemented a new option --x-dem-reuse which allows to copy the DEM file from an older map. My idea is that the option specifies the path to either 1) a gmapsupp or 2) a gmap folder or 3) a directory containing *.img files from a previous run with similar dem-dist option and tile boundaries. If given, mkgmap tries to find the matching *.DEM in any of these formats, checks if the content matches the wanted boundary and dem-dist option and - if ok - uses the existing file instead of doing the DEM calculations again. At the moment I have some working quick+dirty code (see attached patch). I assume the new code in MapBuilder should go somewhere in package uk.me.parabola.imgfmt.app, maybe a new class ImgFinder or so? Or do we already have such code in mkgmap? What I also don't like is that it copies the data from the existing file into memory. Is there already an easy way to avoid that? Gerd