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[mkgmap-dev] Overview of OSM tagging vs effects on Garmin maps

From Colin Smale colin.smale at xs4all.nl on Wed Mar 30 10:42:28 BST 2011


I have been experimenting with mkgmap for a couple of months now. I am 
not really a Java programmer, but I can read and understand the code 
easily. Having been surprised by how certain map attributes come through 
on the Garmin using the standard stylesheets, I have been looking into 
how the chain currently works from OSM data to mkgmap to the style 
sheets to the Garmin device so I could consider adjusting the way things 
are tagged in order to improve the end result. I am of course not 
advocating "tagging incorrectly for the renderer". My intention is to 
optimise routing instructions, including both actual turns and the 
spoken instructions.

Browsing through the code, I have discovered quite a few pieces of logic 
which refer to specific OSM tags which are not, or poorly, documented. 
For example, the "through_route" relation is extremely useful, and I 
have seen that the "display_name" tag can override "ref" and "name". 
Neither of these are documented on the OSM wiki. There are also quite a 
few "internal" tags in the mkgmap namespace which could concievably be 
set in the OSM data to override default algorithms in the code.

Now there's a discussion taking place about revising the documentation 
for the command line options, would it be an idea to start some 
documentation of the way tags are used within the Java code? This would 
assist anyone wanting to tweak the style sheets without diving into the 


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