If you want to tag boundaries representing a closed ring/area please see Relation:boundary
Boundary segments are made with the generic relations: type=multilinestring and are used for grouping ways to form a bigger logical linear boundary making the border between two regions. Such as the border between Italy and France but can also be used on any type of boundaries (administrative, protected_area, military, maritime, etc.)
(See Relation:multilinestring for more details on the construction)
|name||*||The name of this boundary if applicable (ex: France/Italy boundary)|
|boundary||administrative / protected_area / ...|
|admin_level||the admin level|
|Way or Node||Role||Recurrence?||Discussion|
|(blank)||one or more||the multiple ways representing one linear border|
|(blank)||zero or more||Other relations of type=multilinestring could they be boundaries as well or other nature|
The sum of ways + child relations's ways + child's child's relation ways + ... should form a linear connected list of ways
Note : Ways without a role shouldn't form a closed border. For closed border, see Relations:boundary.
Why not use only the closed relation Relations:boundary (or type=multipolygon relations) ?
- Processing time is high and might lead to problems if all the member ways are in one single relation
- Editing is very hard due to huge list of members
- When a boundary segment is created, it can be reused by the two relations forming the two countries/regions
- Easier to represent or use the boundary between two countries/regions as it is only one relation
Why not ?
Why use the current closed relation system?
- it's approved
- a lot of people use it for about six years now
- JOSM is good at handling even the biggest country borders worldwide; the relation editor in JOSM works fantastic, great compliment to the developers!
- It will be harder to verify the integrity of borders (at least this one will stop working: http://tools.geofabrik.de/osmi/?view=boundaries&lon=16.25684&lat=53.66678&zoom=4&overlays=boundary_relations_2)
- A lot of people at this moment rely on the current approved relation system for mapmaking purposes
- It requires an enormous change management project to make this work for all country/region/city etcetera borders
- It doesn't solve the real problem: changing borders should require a verification process by an editor because border relations are broken up too often; OSM is yet (2012) far away from this Wikipedia level of matureness