Changeset: 115462088
improve rivers continuity
Closed by Verdy_p
Tags
created_by | JOSM/1.5 (18303 fr) |
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source | OpenStreetMap Carto (Standard); Bing |
Discussion
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Comment from user_5359
Hello! Please have a look on https://www.openstreetmap.org/way/31262714/. You add the key admin_type:NE. why is it necessary to attach a country code to a technical description? For one thing, both border relations belong to the same country. Secondly, it would actually be information on the border relations and not on the path of the river.
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Comment from Verdy_p
it is the same way for the river (linear relation) and the administrative entity.
So it has admin_level (the smallest admin_level of boundary relations using it).
"admin_type" serves another purpose because admin_levels are not strictly the same as administrative entities (and there are frequent cases where different effective "admin_type" values share the same admin_level (or no admin_level value at all when they are not hierarchic or are in a separate hierarchy): these admin_types are country-specific according to their local definition.
All this has no effect on the river itself (these tags are ignored by them) but have effect on the interpretation of ways, a -
Comment from Verdy_p
and what they are used for: they indicate explictly that the way is used by "some" relations (without saying how may or where) so it indicates that we should look at these relations containing the way to interpret it. It also explicitly indicates that this way should not be removed (or joined) only because it is part of a river way, because it would break the other relations not defining the river itself.
Theoretically we could even drop all attributes from these ways, but experience shows that ways are not always loaded with all relations using them, and not marrking these ways causes relations to be frequently broken by removed/splitted ways or joining that did not have the same attributes. There are a few other purely linear attributes that are also local to each way (e.g. speed limits, width, or attributes marking what is along these ways, i.e. describing the borders of the river or highways, such as lanes, kerbs, retaining walls, fences... and that are not described in the relations themselves because they don't apply to all ways that are members of the relation). So there are tags as well on ways, but for different purposes. We have to play also with compatiblity of renderers or to database queries (it's mor difficult to query the database on objects as it requires querying whar are other objects referencing the described object). A few extra tags on ways do not hurt: they are descriptive, their interpretation still depends on what is effectiely described in the relations using them. But it let "others" be awre of what kind of objects these ways are part of. -
Comment from user_5359
Unfortunately, you have not answered the essential part: Why the country code in the admin_type?!
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Comment from Verdy_p
Because the given value is country specific, bound to its law and has NO equivalent in any othjer country, even if the other country names these types the same way (they don't work the same way, and not necessarily at the same level.
There are many other examples existing already. "admin_type" values are NOT worldwide unifiable, unlike "admin_level" that are OSM-specific and have NO meaning by themselves in any country (admin level is purely an invention in OSM for OSM, which frequently mixes different statuses at the same level, even within the same country, you can find examples just nearby, within Burkina Faso, with the local statuses of its departments as "communes" with different statuses but all at the same "admin_level"; the same occurs in many countries, and in fact in most of them: the hierarchival model of "admin_level" is a OSM simplification for another reality. See other examples in US, Britain, France, Spain, Russia; Germany...: that's where "admin_level" is insufficient and we need country-specific statuses; in same cases there are competing status in areas claimed by several countries or administered jointly; administrative status are complex and have lot of exceptions to the simplified model of hierarchical levels). Adding the country suffix explicitly prohibits unifiying statuses defined only by the relevant country, sometimes even outside of its defined border, so that you can't even use a geometric request to locate all those entities (the same would apply to the country-specific tag set in relations, like it would apply to their member ways.
You'll also find "border_type" used as well but not necessarily for administrative areas (however border_type" is more weakly defined because of this and I've not seen any area in OSM where it as used consistantly; but they persist for legacy reasons as they are used by some applications; but they are much harder to fix without understanding their actual usage in third party apps; however a few usages have been documented in the wiki even if I don't know precisely if they are maintained the same way between those created these documentations and those that added them or attempted to maintain them in OSM data); you can find however a few old interesting talks in the mailing list archives; but for the purpose administrative boundaries, I think that "border_type" is deprecated since long, "admin_type" replaced them, preferably with a relevant country code suffix to avoid artefacts along international borders and to efficently facilitate their use in data queries). Using tsuch suffic is very common for country-specific tags (such as classification of schools, other public services or utilities, or maintenance of external references: there are many tags using a country code suffix appropriately to avoid collisions between concurrent interpretations)
Ways (17)
- Le Niger (31262714), v45
- Gorou Kirey (31276223), v14
- 31616355, v32
- La Sirba (39408765), v9
- 39526656, v6
- 39526757, v8
- 39526759, v7
- Le Niger (201085654), v10
- 238805246, v11
- 238805249, v7
- 264728221, v7
- 838941142, v6
- Le Niger (914800702), v2
- Le Niger (914800703), v2
- Niger (914800704), v2
- Le Niger (914803752), v2
- La Sirba (914803754), v3
Relations (2)
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