Hi all, during the last days I tried to find more about the way how mkgmap stores polygons, esp. why we have some limits. While doing that I stumbled over an old comment in LinePreparer.java: // I don't care about getting the smallest possible file size so // err on the side of caution. which made me curious because I do care ;-) I found out that Garmin offers a "trick" in the delta encoding which allows to reduce the needed bytes in some cases, the imgformat-1.0.pdf explains this in detail, search for " only the sign bit is set ". This "trick" helps esp. well when coastline polygons or rivers are stored. I can explain this more detailed if somebody likes to know more, for now I'd like to hear if the trick causes any problems, I did not find any so far. A binary with this and a slightly improved overview_levels_v2.patch can be found here: http://files.mkgmap.org.uk/download/301/mkgmap.jar Depending on the data a single tile with size ~5MB may be reduced by 50 - 500+kB. Gerd