In the last days there have been two questions around the mkgmap message "Area (xxx,yyy) to (zzz,qqq) contains ... but can't be split further". The message is printed during the subdivision creation process which means a tile is splitted into several subdivisions which do not exceed a special dimension and does not exceed a maximum size (which means a max number of nodes, lines and/or shapes). I have started to look how this works because I think there is some work to do. Such errors will occurr more often with increasing density of map information. The split process does not seem to be optimal. I want to start with a list of questions and observations and hope someone of you is able to answer/comment them or is willing to dive into the source code to get an idea of what's going on there. 1. Class Area definition An area is defined with minLat, minLong, maxLat, maxLong. It is not possible to define an area with minLat==maxLat or minLong==maxLong. Is there any reason for this? 2. Class Area split The split method divides the area into a given number of (rather) equal sized subareas. An area [(0,0) to (100,100)] would be split (xsplit==2, ysplit==1) into [(0,0) to (50,100)] [(50,0) to (100,100)] I think this is wrong, because the two areas are overlapping at x==50. Does anyone know why the split method does not split into distinct areas? 3. Class MapSplitter As far as I understand lines and shapes are put to the subdivision that contain their center points. Assuming the situation (I describe a line example but the same applies to shapes) E ------- + | | + | x | + ------- + + S+++++++++ S = start point of a line E = end point of a line + = line x = center point -| = borders of the subdivision The line is defined in the subdivision although it does not intersect the subdivision. But its center point is located in the subdivision. Is that correct? The coordinates of the line points are stored as diffs to the center of the subdivision as a kind of compression. The diffs have a higher and lower limit. If a line is quite long and one point is far away from the center of the subdivision it could not be stored. What happens in such a case? I think a warning message is printed in the constructor of the Subdivision class but what happens to the line point? Would it be better to split a line in such a case? Or would it be better to split a line so that the complete line fits into a subdivision? 4. Subdivision splitting In case a subdivision is too full it is splitted into equal sized areas. Would it be a good first approach to improve the splitting so that the algorithm tries to split the subdivision into rather equal filled subdivisions (e.g. each splitted subdivision should contain the same number of points plus center points of lines/shapes? Have fun! WanMil