Version mkgmap-r4180 was committed by gerd on Fri, 27 Apr 2018 prevent AssertionError when writing TRE bounds at 180° The value 8388608 doesn't fit into a 3 bytes signed integer. We write -8388608 instead and Garmin seems to expect that. http://www.mkgmap.org.uk/websvn/revision.php?repname=mkgmap&rev=4180