georges wrote > Hello, > I am converting an .osm file to shapefile, and there is one thing that I > do not understand: > > What is the difference between: osm_id and osm_way_id fields (keys)? > > They are defined in osmconf.ini file, but only for [multipolygons]. > Here is an explanation from the osmconf.ini file: > > # note: for multipolygons, osm_id=yes instanciates a osm_id field for the > id of relations > # and a osm_way_id field for the id of closed ways. Both fields are > exclusively set. > Does that mean that osm_way_id will be used to represent the osm id number > of a closed way, while osm_id will only be used for to represent the osm > id number of relations? > > It's a bit confusing concept. > > What makes the closed ways so special so that they need to have their own > special field (osm_way_id)? > Why wasn't there a separate field for relations instead: like: > osm_relation_id, while closed ways would use the osm_id. > > Thank you for the reply.
Indeed, OSM data model is a bit confusing concept. You can read about it from https://wiki.openstreetmap.org/wiki/Elements. Simple, small polygons are usually modeled as a one continuous, closed ring. That makes one "way" and the ID for it is found from way_id. All the other polygons are modeled as relations which are collections of ways and they have "relation_id" in the data as you can see node_id http://www.openstreetmap.org/api/0.6/node/389960161 way_id http://www.openstreetmap.org/api/0.6/way/34028339 relation_id http://www.openstreetmap.org/api/0.6/relation/125519 IDs are unique only for nodes/ways/relations but not across the elements. I do not think that renaming osm_id into relation_id (and probably osm_id of points into node_id, or?) and osm_way_id into way_id to follow the native model would make things very much more clear. -Jukka Rahkonen- -- View this message in context: http://osgeo-org.1560.x6.nabble.com/gdal-dev-osm-id-vs-osm-way-id-tp5298287p5298304.html Sent from the GDAL - Dev mailing list archive at Nabble.com. _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
