Relation:network
 network
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Used to describe networks of various kinds. 
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Status: in use
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The tag type=network is used in some places to tag relations which represent a "network". Most commonly this has been used to map cycling and walking "node networks" in the Low Countries of Europe, and public transport systems in some cities.
The more common tag for public transport routes is a route relation with a network=* tag.
How to Map
A network relation contains the elements that together form the network. These could be route relations, route_master relations, network nodes of a node network, etc.
The network relation has the following tags:
- type=network - specifies this is a network relation
- network=* - specifies the type of network relation: (optional)
- name=* - name of the network
- ref=* - official reference code of the network (optional)
- operator=* - operator of the network (optional)
The members of a network relation are different for each type of network:
- Cycling, walking and outdoor sports networks: route relations and/or superroute relations
- Node networks: route relations and network nodes
- Public transport networks: route_master relations
- Road networks: route relations and/or superroute relations
Controversy over this tag
Use of this relation sometimes violates the principle that relations are not meant to model categories like "all tram stops in Frankfurt".
Advantages
- Network relations group their member regardless of a certain key or feature, as OpenStreetMap does not feature static IDs, the creation of network relations creates a "real" group.
- Each member can be described with a certain role, which is especially useful for network relations.
- Relations are ordered lists. So when the order of members is important, this can be captured in a network relation.
Disadvantages
- Some network relations may become huge as they represent huge network, this may become an issue.
- Especially new mappers repeatedly do not understand that/how they have to add parts of the network to the relation. Therefore, this is not always done properly and requires additional maintenance.
Alternative
The use of the tag network=<xyz> for all members of a network is the most common alternative. One drawback is that the value of the network is often not unique. network:wikidata=* can supplement network=* to disambiguate similarly named networks. Another drawback is that the network=* tag is used differently for bicycle and hiking routes. cycle_network=* exists as a partial workaround for this issue.
Usage and examples
Electricity networks
According to Taginfo, one of the most common roles in network-relations is 
substation. United Kingdom renewable energy describes the usage of this role, but does not mention type=network.
Cycling, walking and outdoor sports networks
- Main article: Cycle Node Network Tagging
- Main article: Walking_Routes#Tags_of_the_relation
The concept of network-relations is used for node networks in particular. This enables grouping of both routes and nodes. Sometimes network relations are also used for normal networks, containing only routes.
Examples:
- 12876306
12876306 - Fietsnetwerk Houten, containing all routes of a cycle network - 7491418 7491418 - Wandelnetwerk Land van Streuvels, containing all routes and network nodes of a walking node network
- 5537385 5537385 - Skateroute-netwerk Midden-Delfland , containing all routes and network nodes of an inline skating node network
Public transportation networks
Network relations are sometimes used in the context of a common fare system, a certain type of transportation and the (subsidized) concessions to operate a number of lines. However, controversy exists whether this usage violates the principle that "relations are not categories".
The Public transport proposal (PTv2) did not make use of network-relations and that route master relations were not network relations.
Dutch approach
Network relations are used to mark the membership of a route to a public transport concession. This is motivated by the ease of maintenance in the light of constant changes in concession ownership.
Examples:
- 5265213 5265213 - Hoofdrailnet Nederland concession, containing the route master relations of all train routes belonging to this concession
- 364180 364180 - Stadsvervoer Amsterdam concession, containing the route master relations of all tram, bus and subway routes belonging to this concession
- 420214 420214 - Noord- en Zuidwest-Fryslân en Schiermonnikoog concession, containing the route master relations of all bus routes belonging to this concession
German approach
The idea of network relations for concessions or fare systems (German: Verkehrsverbunde) was doomed on the mailing list as they change regularly and have no relevance for users. The current situation seems to be that everything is mapped in the route=* or route_master=* relations and network relations are abandoned and ignored (examples: 66263 66263 missing underground line 4, 2664636 2664636 with note=teilen, teilen, teilen, German for divide, divide, divide).
Road networks
Some network relations are used to group route=road relations. This is done in addition to a network=* tag on the route relations itself and could therefore be seen as redundant information. However it could be useful when multiple networks exist parallel to each other.
Examples:
- 7884303 7884303 - International European route network, containing the route and superroute relations making up the E-road network.
- 13290323 13290323 - Rijkswegennet, containing the route relations making up the national road network of the Netherlands. The route relations themselves use network=NL:A and network=NL:N, the A-road and N-road networks, which exist parallel to the Rijkswegennet.
See also
- Relation for a general overview of this data primitive.
- Types of relation lists different types of relations and related proposals (even abandoned and rejected ones)
- Key:network describes the network-tag itself.