A bridge is an artificial construction that spans feature such as a road, railway, waterway or valley and carries a road, railway or other feature.
Use bridge=* to identify man-made structures used to carry a road, railway, path canal or similar over another feature or across a valley by use of a deck or arches (see below for when to use tunnel=*). A list of bridge types is given below which includes viaducts, swing-bridges and pontoon bridges.
Where the lower feature is surrounded by earth then the lower feature should probably be tagged using tunnel=* instead. It is sometime, however, a matter of judgment as to whether to tag a particular situation using a bridge or a tunnel. Do however avoid using both a bridge tag for the upper way and a tunnel for the lower way for the same crossing.
How to map
Split the upper way at each end of the bridge (which is where it joins solid ground) and add bridge=yes to the central section. It is good practice to not let a bridge terminate at a road junction or similar. The bridge should either end before the junction (the normal situation) or in cases where the junction is actually 'in mid air' itself then the other ways joining the junction should also be made into bridges for the relevant sections.
A ramp at an end of a bridge is not part of the bridge and can be tagged as embankment=*. An embankment should not have a layer tag in most cases.
If the bridge has a maximum weight or length then add a maxweight=* or length=* to the upper way. If there are restrictions of the class of vehicles or users of the bridge use the access=* tag. A link to a Wikipedia article should be placed in wikipedia=* using the format <language code>:<page title> and choosing the primary language for the article (Wikipedia can handle the multi-language links); for London Bridge the tag would be wikipedia=en:London Bridge. The construction date can be put in start_date=*.
Where the bridge has a name there are a number of options for tagging. The one chosen is partly personal choice but may also depend on the significance of the bridge:
- Use the name field itself to hold the name of the bridge rather than the name of the road itself. For example London Bridge, in London, is named 'London Bridge' in OSM  and . The southern approach is named 'Borough High Street' and to the north the road is known as 'King William Street'. By way of comparison tthe Ordnance Survey have half of the bridge named 'Borough High Street' in OS Locator and Google Maps names one direction Borough High Street and the other direction London Bridge (Jan12). In reality the bridge probably has a road name and a bridge name and the road name probably does legally change in the middle of the bridge. This approach has the advantage that it will get rendered.
- Use the street name for the name field and put the name of the bridge in bridge:name=* as has been done for Stoke Bridge in Ipswich where both approaches to a minor named bridge are the same. By way of comparison Google also calls it Bridge Street.
- Use the proposed Relations/Proposed/Bridges and Tunnels to hold the bridge name.
- The proposed man_made=bridge can be used to hold bridge specific-attributes like name, reference, etc.
If the bridge has former names these can be tagged using bridge:old_name=*. A bridge reference can use bridge:ref=*. When using the proposed relation or man_made=bridge the keys old_name=* or ref=* can be used.
Don't use the tag building=bridge just for for marking bridges (their outlines). For such purposes you can use the proposed man_made=bridge. The tag building=bridge refers only to buildings, which are used as bridges.
Bridges with several roads/ways or additional features
In case a bridge is represented by several ways or carries additional features there are currently two proposed ways to indicate this:
- With the proposed man_made=bridge simply the outline of the bridge is drawn. The roads/ways passing the bridge are connected to the outline. All bridge-specific attributes like layer, name, reference, etc. can be tagged directly on the outline. In case of bridges with multiple levels the proposed relation bridge has to be used additionally.
- When using the proposed relation bridge all features of the bridge have to be members of the relation and all bridge-specific attributes can be tagged in the relation. In case the bridge has multiple levels only the relation can be used in order to group together all objects of the bridge.
See below for a longer list of values in the proposals section.
|bridge=yes||A short bridge and for non-specific bridge tag.|
|bridge=abandoned||Ruins of a bridge. Typically abutments and piers are all that are left, however, the bridge could be collapsed. Implies access=no.|
|bridge=aqueduct||A longer structure for carrying a canal or fresh water. Consider using historic=aqueduct for significant ancient aqueducts.|
|bridge=cantilever||A bridge where a span is supported at one end only. Usually, the free ends of two spans are fastened to one another, giving a longer clear span between supports.|
|bridge=covered||A covered bridge has a roof and fully or partly enclosed sides, usually to protect the bridge deck and members from deterioration.|
|bridge=low-water-crossing||Also known as an "Irish bridge", this is a low bridge which is engineered to carry vehicles above water at low flow levels and survive submersion at high flow levels. Consider also adding either ford=yes or flood_prone=yes on low-water-bridges that will sometimes be flooded on a seasonal and/or intermittent basis (see Discussion page).|
|bridge=movable||Movable bridges contain a span that can be moved up or to the side, often to provide greater clearance for traffic moving beneath the bridge. All such spans should be tagged with bridge=movable. Further information may be provided using bridge:movable=*. The fixed spans should be tagged separately, to make clear which part of the bridge is and is not movable.|
|bridge=trestle||A bridge composed of a series of short spans where each span is supported by a rigid frame, usually called a "bent" rather than a pier.|
|bridge=viaduct||A bridge composed of a series of short spans. The spans may be arches, girders supported by piers, etc. For ways or features that raise a feature above the natural ground on mounds or earth walls, use embankment=*.|
Here is a longer list of proposed values (some of which don't currently render as bridges on the main Mapnik map view):
|bridge=arch||A bridge supported by brick or stone arches|
|bridge=bascule||For moveable bridges with a counterweight that continuously balances the span, or "leaf," throughout the entire upward swing in providing clearance for boat traffic.|
|bridge=cable-stayed||A bridge supported by wires from towers, to be distinguished from suspension bridges. |
|bridge=drawbridge||A movable bridge typically associated with the entrance of a castle surrounded by a moat.|
|bridge=humpback||A name for a type of bridge, specifically an arch bridge, where the span is higher than the ramps on either side, forming a hump-like arrangement. Also 'moon bridge' in Japanese and in Chinese.|
|bridge=lift||For a bridge that can lift out of the way |
|bridge=pontoon||A bridge that floats on water and in which barge- or boat-like pontoons support the bridge deck and its dynamic loads.|
|bridge=suspension||A bridge supported by wires from towers, to be distinguished from cable-stayed bridges. |
|bridge=swing||A bridge that can swing out of the way |
|bridge=user defined||All commonly used values according to Taginfo|
- Relations/Proposed/Bridges_and_Tunnels. This enables the grouping of several ways using the same bridge. The relation also enables tagging a reference number for the bridge.
- Use the proposed man_made=bridge for grouping of all features of the bridge (especially multiple ways) and tagging bridge-specific attributes like name, reference, etc.
- Proposed_features/Bridge_Name - proposal for the name of the bridge itself
- Proposed_features/aqueduct - a proposal for historic aqueducts