[mkgmap-dev] Problem with names of relations

Wed Sep 26 19:27:29 BST 2012

On Wed, Sep 26, 2012 at 06:47:04PM +0100, Roger Calvert wrote:
>It would be helpful if some workround could be found in mkgmap. All the 
>other renderings I have looked at seem able to handle it. If the 
>relation name and the polygon name (or other tags) are different, I 
>agree there is a problem. But if they are the same, I don't think the 
>result should be that the polygon loses its name completely.

Even in cases where mkgmap is able to do some guesswork, it could be 
useful to log a warning, so that these ambiguous relations can be fixed.

I have seen a similar problem with landuse multipolygons. Someone 
imported huge amounts of very inaccurate landuse data from the EU Corine 
to OSM in Finland. He simply ignored existing polygons, so that we can 
have almost-common lines for lakes and forests. Or, we can have forests 
partially overlapping lakes, or one landuse polygon overlapping multiple 
islets and the waters between them.

To add insult to the injury, the import used the old definition of 
multipolygons, where you would duplicate the same tags on both 
role=outer and role=inner ways. This breaks in many ways if some mapper 
thinks "oh, this inner polygon is not a forest, but a farm". (With the 
old definition (duplicate all tags on all members), the correct solution 
would have been to define another polygon on the same nodes, with the 
tags of the inner area. The new multipolygon definition allows us to 
reuse the same way for multiple multipolygons.)

When mkgmap has complained something about these multipolygons, I have 
fixed the problem and at the same time moved all common tags from the 
multipolygon ways to the relation itself.

Best regards,

	Marko