I have done some tests with BuildDEMFile (thanks Frank for providing it!), but with some problems. I have followed the procedure described by Gerd at [1]. What I have done is the following: 1-Try to generate a DEM for my Western-Sahara map with command wine ../../../../DEM/BuildDEMFile.exe --usedummydata=true -d 55132001/55132001.DEM --hgtpath=../../../../DEM/hgt/ --tre=55132001/55132001.TRE --dlon=0.00027761 Result: Daten aus der TRE-Datei '55132001/55132001.TRE' gelesen Höhen für -18° .. -17° / 20° .. 21° eingelesen ... 1 Zoomlevel erzeuge 31594 x 25790 interpolierte Höhenwerte für den Abstand 0,00027761° x 0,00027761°... Out of memory BuildDEMFile was using about 1 GB RAM when it stopped, while there was ~2 GB free available on system. How can I allocate more memory for BuildDEMFile? Western Sahara is very low mapped, so that a large area fits in a single img, but it covers 80 hgt files. Is there a size limit for DEM files and thus large areas should be split for img generation? 2-Try to generate a DEM for my region (Extremadura, Spain) with command wine ../../../../DEM/BuildDEMFile.exe --usedummydata=true -d 55113002/55113002.DEM --hgtpath=../../../../DEM/hgt/ --lastcolstd --tre=55113002/55113002.TRE --dlon=0.00027761 Result: Daten aus der TRE-Datei '55113002/55113002.TRE' gelesen Höhen für -8° .. -7° / 37° .. 38° eingelesen ... 1 Zoomlevel erzeuge 10560 x 9339 interpolierte Höhenwerte für den Abstand 0,00027761° x 0,00027761°... Daten 10560 x 9339, Min. 70, Max. 2577 für Zoomlevel 0 Value cannot be null. Parameter name: destinationArray What does it mean and how to fix it? 3-Try to generate a DEM for an small portion of my region (only 4 hgt files required) with the same command as previous Result: DEM created. [1] http://www.mkgmap.org.uk/pipermail/mkgmap-dev/2017q4/027176.html