Gerd's comment about looking at the overview map, prompted me to look at mine, and I realised I didn't have one (or it is empty), despite me having --tdbfile specified - the help for this option says an overview map will be created. I assume I am not getting an overview map because I don't have --overview-levels specified. Would it be better if the default for --overview-levels is not an empty string when --tdbfile is specified? The documentation for --overview-levels is not very clear. From inspecting the code it looks like the format expected is similar to the format expected by --levels and that the overview level numbers should be greater than the normal levels. Can the documentation for this be improved? Also, what is the benefit of specifying something like --overview-levels=5:15,6:13,7:11 over the much simpler --overview-levels=15,13,11 and have mkgmap work out the next free levels. Could we simplify this? Regards, Mike