[mkgmap-dev] Want to make one map from individual maps with different details

I noticed that Garmin City Navigator uses different thickness of linetype as you zoom out. I can create 2 different TYP files (filename.txt) to be used with my mkgmap command and still use the same style files, but I do not know how to combine these different maps and how to specify at what zoom levels each map is to be visible. Example: Zoom level 0-2 (detailed map with wide roads 'detailed.img') Zoom level 3-5 (overview map with thinner lines and some features removed 'overview.img) How exactly to I combine these 2 maps into one 'combo' map. I know the file size will double Do I use GmapTool? Greg