I know a lot of people have a problem with OSM objects not having a dependable unique identifier. Of course, a node has an ID which will never change. But a campsite mapped as a node will get a very different ID when someone decides to re-map it as a polygon. This makes life complicated for external applications who would like to link up their data to OSM. For example, a fabulous application like iOVerlander (collects data, reviews and ratings on wild/formal campsites) might want to make all the campsites available in OSM rateable in their application. But it would be silly to also copy the geography to their database - as OSM geography is improved upon all the time. Of course, [there’s a fuzzy way to refer to a specific object] (http://wiki.openstreetmap.org/wiki/Overpass_API/Permanent_ID), but that’s really of no use in this case. Imagine a campsite without a name. Then you could tell OSM to look for a campsite within a certain radius of where you found it. But what if a new campsite has been added? What if the campsite has gotten a better coordinate? What if it has become a caravan site. Etc… Or a more complex case: take a bar that has moved locations. Do you give preference to the location or to a bar with the same name somewhere else in town.

This would be an argument to just include much more data within OSM, as that way the link between the thing and its description cannot easily be broken. But considereng even adding some price information is controversial, adding opinions etc. would be unthinkable.

As I’ve been playing with the idea of using Openstreetmap as a base for an open alternative to Tripadvisor, I’ve been thinking about this problem a lot. In a flash of inspiration, I thought of this concept. I would like to hear some opinions about that. Anyone who has a project that requires a thing to have a unique ID can look it up through a query to an www.osmdata.org . All objects that have linked external content, get an extra tag, for example “osmdata=uniqueid01”.

Here’s how it could work in practice. Imagine a site where all things vaguely related to tourism are searchable and clickable on the map. Take restaurants as an example. Or generate a list of all restaurants in a city. This list can be updated automatically all the time. But once users start adding untaggable information, like “overpriced” or “what a lovely atmosphere”, this data will be saved outside of OSM. Instead of forking the location, the restaurant gets an extra tag in OSM (osmdata=uniqueid22), and the bits of external data saved outside of OSM get this same ID. Now when someone moves the restaurant in OSM (copying tags or dragging the node and deleting the old node) nothing gets messed up. When someone re-maps the restaurant as tags on a building, they copy the osmdata tag too, and again nothing is broken. If a different project wants to use the same thing, they just use the same osmdata unique id. That way, database bloat is minimal.

Another example would be to rate subjective features of roads, like how scenic are they. The same principle could applied; and the result could be Michelin-style maps with a green outline for crowd-approved beautiful trips.

Of course, a side-effect will be that external projects like iOverlander would have a much easier time building their project around OSM data. Which would mean that their users would contribute to OSM, instead of just to the external project.

I’m very interested to hear your ideas on how this problem could be solved - or how it is not a problem - or how it has been solved before