Good practice

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OpenStreetMap is a free project done by volunteers. Anybody can enter anything he or she wishes. That said, a map works best when participants agree on a code of conduct. These "Good Practices" are guidelines that will increase the quality and value of our map data without any additional effort. Nobody is forced to obey them, nor will OSM ever force any of its mappers to do anything. There might be cases where these guidelines don't apply, or even contradict each other.

Do correct errors

If you find elements with tags that you think are wrong then do correct them. It's a wiki, your corrections can always be reverted, so be bold.

Map what's on the ground

Sometimes there's conflicting information about, say, the name of a place. An old map might call it one thing, current maps another, and the place name sign something else. People using our maps (for navigation) won't care about the spelling in other maps, they need to find the names from local signs in the map and vice versa. The only exception to this could be obvious misspellings on signs like John-F.-Kennwdy Square. Assuming that people would intuitively look for the correct spelling it makes sense to correct these.

Naming conventions

Don't use abbreviations

Don't describe things using name tag

Unnamed objects

Objects (usually streets) which have no name:

  • without name=* or it's variants
  • additionally could be tagged noname=yes

See also

Good changeset comments

Main article: Good changeset comments


Main article: Verifiability

OSM data should, as far as is reasonably possible, be verifiable. The principle applies to tags and other aspects of data representation, and essentially means another mapper should be able to come to the same place and collect the same data ("verify" the data you have entered).

Don't map historic events and historic features

This is a consequence of the verifiability requirement. Do not map historic events. Do also not map objects if they are not there anymore because such features can not be verified. Historic events have been discussed here. If ruins are left (and thus verifiable), then map the ruins (for example using historic=ruins). There seems to be agreement that abandoned and dismantled railways may be mapped if at least some traces are left (use for example railway=abandoned). Abandoned and dismantled railways were discussed here.

Don't map your local legislation, if not bound to objects in reality

Things such as local traffic rules should only be mapped through the objects which represent these rules on the ground, e.g. a traffic sign. Other rules that can not be seen in some way should not be mapped, as they are not universally verifiable.

Don't map for the renderer

Main article: Tagging for the renderer

Draw things the way they are on the ground and don't care what the renderers make out of it. They are continually improving, don't bend the data to make it look prettier, just be patient.

a lot of tracks named "track" (in German)

Keep the history

When things change in the real world, be bold, and edit the map to reflect the current situation. But be aware that OpenStreetMap can store the editing history of an element, and you can help preserve this history by making sure you re-use one element when it becomes something different. Example: If a café closes down, don't delete the node. Just remove the cafe tag, and leave other tags (like the address) in place.

When updating buildings or landuse you may wish to delete and redraw anew, but to retain an editing history it may be better to edit existing objects. For JOSM there is a tool "replace geometry" in the plugin utilsplugin2. With this you can draw a new outline of the object and then merge the outlines shape to the existing way.

One feature, one OSM element

Main article: One feature, one OSM element

Don't place nodes in identically tagged areas just to see some icon appear on the map. The renderers will display icons on areas as well and there's no need to have every parking-lot, soccer-ground, etc., duplicated in the database.

Keep straight ways straight

Main article: Editing Standards and Conventions

When there's a road that's dead-straight, draw it as such. That's done by just one line between two nodes without any nodes in between. Some roads are perfectly straight even when your GPS-track might think differently.

JOSM, iD and Potlatch all have tools to straighten streets with intersections. That keeps our data slick and makes the maps look better. Having said that, if you have multiple traces for a particular road and they all show a bend in the road, or you see the road's shape in an aerial photograph - then depict this shape in OSM.

Map bends with an appropriate number of nodes

Ensure you use a reasonable number of nodes to record bends and other features. There's no hard or fast rule about how many nodes should be used to map a bend in a road - you need to use your own judgment - but there should be enough so that the angle between successive parts of a way should not be too large (e.g. shouldn't be close to 90°). This means that on sharper corners - the nodes will need to be closer together to map a smooth curve in the road than on relatively shallow corners.

Average out GPS-traces

Main article: Accuracy of GPS data

The accuracy of the points in a single GPS trace may be out by several meters. This depends on lots of factors such as the positions of the satellites when the trace was taken, tree cover, proximity to nearby buildings, position of the GPS unit relative to the center of the road etc. If many traces are taken for the same road, then the effect of errors in any one trace will have a much smaller impact on the average position of these traces.

To help with this, it's useful if you upload all traces to the server - even if they cover roads already in the database. This allows others to use your traces to average out the errors and should eventually result in lower position errors. If you have many tracks covering the same way, you may also try the "average tracks" script to make one "average" trace.

Mark estimations with FIXME

Sometimes it makes sense to map estimated positions rather than not mapping the object at all. But always mark your estimations with a fixme=* so you or somebody else will come back to it.

Don't remove tags that you don't understand

Sometimes you will come across elements with tags that have no meaning to you. This doesn't automatically mean you should remove them. They may have been added for a specific purpose. If you think they might be junk then try to contact the author.

Document your custom-tags

Main article: New Features

When you use tags yourself that aren't on map features, give other mappers a chance to understand (and maybe adopt) them by documenting them in the wiki.

Don't over-use semi-colon separated values

Semi-colon value separator characters can be introduced into values, where the same key needs to take multiple values. This can be useful for putting lists of values into certain type of minor attribute tags, however it should be avoided in more important top-level tags. In general these special characters should not be over-used, since they detract from the simplicity of the tagging system.

Various advices

See also