On Wed, Jan 2, 2013 at 8:16 AM, Chris Hill <o...@raggedred.net> wrote: > On 02/01/13 12:50, dies38...@mypacks.net wrote:
> Whoever told you that is wrong, not that that is unusual on mailing lists. There are many people (myself included) who believe that source /on objects/ is not useful, and most OSMers have moved away from using it, and toward source on changesets. Much like created_by, source is a meta-information tag. That is the tag describes data not about the object, but about its collection. We, I think, can agree on that. So then the question becomes "Where does one store metadata?". At first, we as a community stored all metadata on OSM objects. But if you look at an object's history, you see the problem with source. Let's say we have a way 1000. It's a closed way. It's only tag is building=yes. They got the building outline from Bing imagery. So now we'd have: building=yes source=Bing Then another user comes along and walks outside the building, and sees its name. name=Joe's Restaurant A third user comes along and sees that Joe's Restaurant hasn't been tagged with its function, and adds: amenity=restaurant cuisine=seafood You start to see the problem? The source tag no longer gives you a complete picture. The name and classification data don't come from Bing, but the classification doesn't come from local knowledge. So then what do we do? We could have a source tag for every tag... source:cuisine ? Do we really want that? What if we have that, and Joe's Restaurant turns into a steakhouse? What about all those source tags? Contrast with what many (most) mappers do. If they include a source at all, they put it on the changeset. This is a source for the change, or set of changes. So we'd see the object's history, and we'd see the original building outline. Source for that- Bing. See the name added. Source for that- surveying See the clasification. Source for that - local knowledge. See the new classification. Source for that- local knowledge (different user). And so on. In addition, the user no longer has to keep track of all those source tags on the object. That is why most mappers have moved away from source on the object to source on the changeset. This isn't a proposal- it's what most of us do now. > Firstly, you can use any tag for any purpose on OSM, so adding a source=* > tag to an object is _always_ acceptable. In a free tagging system like OSM, everything is acceptable. Even created_by is /acceptable/, but it's generally not done anymore. > Secondly, any changeset can have multiple sources so adding the source tag > to a changeset is not flexible enough. We use semicolons for all tags as a separator. > Thirdly, if the source tag is on a changeset, in order to find the source of > an object you have to look up the changeset(s) that affected the object to > determine its source. Who would bother? I do all the time. I want to know who made what change- either to tags, or geometry. If you can't be bothered to hit Ctrl-H, you can't be bothered to type in the latest "source=foo" tag either. There's no big fight, but there are evolving tendencies in OSM, and much like all tagging- there's no right or wrong, but there are patterns which we seem to follow- which make it easier for others to work with. - Serge _______________________________________________ Tagging mailing list Tagging@openstreetmap.org http://lists.openstreetmap.org/listinfo/tagging
