Version mkgmap-r3816 was committed by gerd on Mon, 20 Feb 2017 change ShapeMergeFilter so that it produces predictable results The previous algo used iterations over HashSet and IdentityHashMap.values() which do not garantee any order. The new algo should produce equal results for equal input so that two runs of mkgmap with --preserve-element-order will produce img files which only differ in some timestamp fields. http://www.mkgmap.org.uk/websvn/revision.php?repname=mkgmap&rev=3816