On 30/09/2012 19:46, WanMil wrote: 
The mkgmap multipolygon algorithm removes all tags from the outer ways 
that are identical to tags of the relation. Therefore the tag name=High 
Dam is removed from the way 4798060. (By the way, tagging the 
multipolygon only with name is definitely wrong. Either add all tags or 
no tag to the mp). Removing tags from the outer ways is required to 
handle all mps where the tags are set on the map *and* on the ways. 
These are a lot (best example: all boundaries).

I don't see a good alternative to this algorithm as long as the OSM 
datamodel does not ensure any multipolygon correctness.

WanMil
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WanMil,
Thanks for the explanation. It seems that this process is needed, at least in part, to make sense of incorrectly tagged data. There certainly will always be incorrectly tagged data, which programs such as mkgmap and renderers will have to interpret. But is there any way that the deleted tags could be retained in some form for access in the style files? Perhaps they could be re-named along the lines of 'deleted:name=High Dam' .

Roger 
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Roger Calvert