I saw your request for help on the DIME mailing list. I took a look at the DXF file and it does have a lot of "extra" lines in it, as Andrew mentioned. It looks like the "thick" lines are actually rectangular blocks that are filled with small hatch lines. There may be a way to simplify the DXF. I have DXF geometry manipulation code that I have been working with over the last few years based on DIME. If I get to it I may try to write something to simplify the whole file. The source data is pretty amazing in terms of how much detail there is. I have been to Prishtina before, so I am curious.