Change request / adding a feature to the default OSM Map style

This question seems straightforward but there are several components, so let's break them down:

What tags get rendered?

The first thing to remember when thinking about this is that there isn't a single answer. There's the default style on www.openstreetmap.org, we call that the Mapnik style or sometimes the Default style. But that's just an example. Other consumers of OSM data, including the OpenCycleMap, Mapquest and Bing, all use their own styles, and they choose what gets rendered there.

Customizing Rendering

So then the next logical question is, "Okay, the OSM Mapnik style is only one example, but that's the one I care about, how do I get my changes applied there?"

To that there are generally two answers.

1. Request it
   If you want a change made, you can request that change through the bug tracking system at http://trac.openstreetmap.org (you'll need an account there), and then submit a ticket to the Mapnik component.

2. Make the change, show it works, and submit it as a patch.
   This is the more complex way, but it gives you a larger change of success. You must first follow the directions on the wiki for making a map with Mapnik and customizing it.
   I'm not sure what stage the transition of the stylesheets are from svn to git, but the stylesheets are also available at the osm github account, where you can freely fork it, and then make a pull request, which IMHO is the best way to work with the repositories.

Get to know the community

Lastly, OSM is a relatively small and I'd say people-focused project. Your patches are more likely to be accepted if you actively engage the community by joining the dev list or joining us on IRC, giving everyone a chance to meet you, for you to meet them, and the opportunity for collaboration.

The first thing you have to check is to see if it is the primary way of taging and that there are enough elements in the database to make it appear on the map. You can use taginfo for this. In your case tourism=artwork comes up over 6000 times and is the primary tag for artwork.

Next you search in trac for any existing bugs for this tag. If there are none login and open a new ticket.

You can now try and make an icon according to the specifications and see how this would look on the map at different zoom levels. Attach the icon and the example rendering to the bug report and make a comment saying how this could be rendered at different zoom levels.

The rest of the work needs to be done by a developer. If you want to try yoursef as a developer and help out you can try install mapnik, make the change on your computer, test it, make a patch and attach it to the ticket. This will make it easier for the core developers to make the changes.

If the core developers agree with your suggestions and you have made it easy for them to implement, then they will implement the changes and the tag will be rendered.