Hi Gerd Since downloading loading britain-and-ireland-latest.osm.pbf I had been unable to build a gmapsupp because of running out of heap (my hardware is 32 bit, -Xmx1540M is largest value allowed) My problem is mainly because I have 1731146 cities (along with 1046096 streets) Looking at Mdr5 processing, I've changed it in 3 ways to improve memory usage and garbage collection. 1/ use trimToSize() after all the cities are loaded from the individual tile .img. I presume that the growth factor gradually increases as it runs out of allocated array space. I had to change the declaration from List<Mdr5Record> to ArrayList<Mdr5Record> to allow this, but I can't see any problem in this. 2/ Move the main part of preWriteImpl into its own method so the first sortKeys ArrayList and Sort can be freed before calcMdr20/1/2() each create another massive SortKeys and Sort. 3/ Move the scope of mdr20s to a class variable. This is referenced by all the Mdr5Records and the scope of where it was declared before seemed to to cause the garbage collector major problems - it churned for 5 mins using all the processors before running out of memory. After moving it, the whole of mdr is built in a couple of mins with cpu usage mostly < 125%. Ticker