Tags

Tags, consisting of a 'Key' and a 'Value' can be associated with either elements (nodes, ways and relations) or changesets. Both the key and value are free format textual fields, although in practice there are agreed conventions of how tags are used for most common purposes.

Keys and values

Here a a few examples of how keys and values are used in practice:

• highway=residential (a tag with a key of 'highway' and a 'value' of residential which should be used on a Way to indicate a road along which people live.
• name=* (a tag for which the value field is used to contain the name of the particular street
• maxspeed=* (a tag for which the value is often a numeric speed, either in km/h (or in miles per hour if a suffix of 'mph' is provided). SI units do not need to define units, other units, such as miles per hour, knots, yard or pounds should do. Where a regulation is specified in a particular unit then that unit should be used within the value field.
• maxspeed:winter=* (a key which includes a Namespace for 'maxspeed' that indentifies a different value for maxspeed that applies in the winter.

Finding your tag

The following resources are often used to find an appropriate tag or explore tag usage:

• Map Features (a extensive list of the the most commonly used tags)
• Mapping projects (a list of specialist interest projects each with a page describing the relevant tags)
• Taginfo (A useful site to exploring current tag usage, including tag values that are not necessarily documented)
• Tagwatch (A similar service)
• Tagstat (and another)