Talk:Tag:traffic sign=city limit
Ambiguities : city limits within the same urban area, entry/exit, application of restrictions, effective boundaries...
There are cases where city limit signs are present within the same urban area, when going from one city to another. In this case there are usually (but not always) two signs on top of each other : one for marking the exit of one city/town/village, another marking the entry to the next city/town/village.
As these signs imply driving restrictions such as speed limits, it is not clear if this marks the end of the restriction. As well, marking only a node (usually on a highway or frequently just beside it) does not clearly indicate on which part of the highway the restriction applies.
Frequently as well, you'll find an entry sign in one city, but the exit sign will display another name (or the same name with distinct precisions added): this is frequent in rural areas where the same small village is split into several parts belonging to distinct administrative units. Which value should we indicate for the name ?: if the traffic sign includes a precision, it should be present, but the complete name will not match any place name, as it will be composite, e.g. (this layout looks like a French agglomeration entry sign, with a smaller yellow sign on top, for the highway reference number):
|in 1st agglomeration (main)||in 2st agglomeration (exclaves)||in 3rd agglomeration (main)|
Note that the precision of the commune shown in italic and smaller font below the local place name may be partially abbreviated or lowercased (in some cases, the main place name may also be abbreviated or shown in smaller fonts on common words like "SAINT", "LE", "DE"; however the most significant words in the local place name of the agglomeration will be capitalized; local place names in non urban areas such as hamlets are not using this emphasis and don't even use the same colors as they are purely informative and they imply no change in driving restrictions: they are not "city limits")...
This would give the tag "name=Le Village-Local-Name1 (commune de La Ville-Name2)". If you look for the administrative place name (commune), you'll find only "La Ville-Name2" (in this example), but the urban area of "La Ville-Name2" itself does not include this part of "Le Village-Local-Name1" which could be exclaved. Note that in such villages split onto several municipalities, there's frequently no city limit on their separation which may be in the middle of the same urban street (this case occurs on small agglomerations with houses all along the same single axis, or the separation is on a bridge over a small river or on a minor cross road; house numbers are not necessarily discontinuous, and the street/road keeps its local name or reference number) ; the toponyms on city limit signs may remove hyphens and long names may wrap on several lines.
Finally note that not all highways may have these signs (minor roads for agricultural use or driveways with private/restricted access may cross these limits without any explicit markup and there's not necessarily those sign at end of these private/restricted highways).
The tag also does not explicitly differentiate the entry and exit signs (which may not always be located at the same place on a bidirectional highway): I suppose that this tag is only relevant for the entry sign (if there's no entry sign in one direction, but there's an exit sign in the other direction, we could place the tag there as if it was an entry sign).
For these reasons, the speed restrictions (or other applicable restrictions) should be explicitly set on relevant segments of highways (using limits of landuse=residential/commercial/industrial would be very unreliable as these landuse are frequently different from the legal boundaries marked by these signs).
Some contributors may also want to create true boundaries (relations) for "urban areas", but there will be a confusion with urban areas created in official national statistics: the local municipalities may decide to apply restrictions differently along some highways, by placing such city limit signs elsewhere than an the official urban area. As well there are frequently several types of urban divisions in national statistics data (and each country may use their own definition of these statistical or economical urban boundaries for different purposes: "urban area", "urban zone", "agglomeration", "urban pole"...).
So I just suggest that this traffic sign tag only indicates the visible physical presence of the traffic sign, and no other interpretation. We should not need this tag for delimiting restrictions, or any statistical/economical boundary: as it is, this tag is merely and only informative, but unusable in practice for anything else than at the node itself (just like the admin_centre node in boundary relations) as we cannot really determine its applicable area.
Ideally this tag should also indicate from where it is visible, but unfortunately the tag indicates no orientation (and it is not clear which direction to indicate: facing direction to the viewer, or direction of application, or anoother direction if the sign is placed beside the road)... The description also does not explicitly states if the node should be on the highway (often virtually) or beside it (more realistic on the ground, except if it is suspended above the highway, and nothing about the type support: on a vertical pole, attached to the trunk on a tree or fixed on a side wall, or below a bridge or entry of tunnel, or suspended on a cable...)
Map renderers may exhibit some icon, but its interpretation will still be left to the viewing human. Most renderers will simply ignore this tag.