Key:bridge
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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.
Properties
Used combinations in
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bridge=* is used to identify man-made structures used to carry a road, railway, path canal or similar over another feature or across a valley.
A short bridge is generally tagged bridge=yes, whereas bridge=aqueduct is used for longer structures carrying a canal or water and bridge=viaduct is used for most other longer structures. Some aqueducts are better tagged using historic=aqueduct.
bridge=swing is for bridges that move to avoid obstructing vessels of vehicles using the lower feature. Where the bridge has been abandoned and only the abutments still exist use bridge=abandoned.
Where the lower feature is surrounded by earth then the lower feature should be tagged tunnel=* instead. It is not always clear whether a particular crossing is a bridge or a tunnel, but it is best to choose one approach and avoid creating a bridge for the upper way and also tunnel for the lower way.
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.
For many bridges it is appropriate to add a layer=1 to the upper way. For complex bridges layer values of 2 and higher may also be used. A ramp at an end of a bridge is not part of the bridge. A ramp can be tagged as embankment=*. An embankment does not need a layer tag because the way is at 'modified ground level'. 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 [1] and [2]. 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[3][4] 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.
If the bridge has former names these be tagged using bridge:old_name=*. A bridge reference can use bridge:ref=* or using 'old_name' and 'ref' in the relation.
If there are height limits for vehicles using the lower way then add height=*, maxheight:marine=* to a node or a sport length of the lower way.
Values
See below for a longer list of values in the proposals section.
| Purpose | Category |
|---|---|
| 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=viaduct | Longer structures supported on pillars. See embankment=* for earth mounds that raise a feature off the natural land height. |
| bridge=user defined | All commonly used values according to Taginfo |
Proposals
Proposed values
Here is a longer list of proposed values (some of which don't currently render as bridges on the main Mapnik map view):
| Purpose | Category |
|---|---|
| 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=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=covered | A bridge with a roof. Typically used to protect the bridge from weather. |
| 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 |
| bridge=swing | A bridge that can swing out of the way |
| bridge=viaduct | Longer structures supported on pillars. See embankment=* for earth mounds that raise a feature off the natural land height. |
| bridge=user defined | All commonly used values according to Taginfo |
Other proposals
- 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.
- Proposed_features/Bridge_Name - proposal for the name of the bridge itself
- Proposed_features/aqueduct - a proposal for historic aqueducts
See also
- Approved features/bridge - discussion and voting for extension of values
