On 24 Apr 2008, at 13:23, Steve Hill wrote: > But in common software, do the objects have an explicit type? In > OpenStreetMap they do not - the type is determined by a bunch of > arbitrary > tags, for which you need background knowledge of which tags define the > object type and which just define attributes (e.g. there is no unified > "type" tag which you know will always define what the object is).
Fortunately there aren't actually that many noun-type tags (i.e. object type), so you can just check against a small, predefined list. I make it highway and all the other -ways, power, man_made, leisure, amenity, shop, tourism, historic, landuse, military, natural. Anything else you can safely assume is an attribute. As it happens, for 99% of purposes, you'd have to filter by type anyway (if you're doing a small-scale highway map, you won't want shops or power lines), so it's no extra coding burden. It kind of goes back IMO to the principle of having a structure optimised for easy editing, and expecting the users of the raw data (who'll all have different needs anyway) to do some post-processing; and how it would be good to offer some standard libraries which do common post-processing tasks, so you didn't even need this small amount of "background knowledge". But that's best done by someone with more l337 Perl/Ruby/Python/whatever skills than me, I'm afraid. cheers Richard _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
