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Is it possible to split a lake between several ways? This is useful if different parts have been surveyed in different ways (e.g. aerial photography for most of the shore, but GPS tracks near a town). /januari 1st 2009 user:Bruce mcadam

Not that I know, but you can see the source code for osm2pgsql and Osmarender if you want to know. Erik Johansson 13:00, 22 March 2009 (UTC)
Use a multipolygon relation with multiple 'outer' components.--Hai-Etlik 02:21, 24 January 2010 (UTC)

Throwing away good data and confusing the data model

"Redundant tags should be removed from the Way" : this is bad advice. If you do that it makes certain operations much more difficult later on. Also it is mixed abstraction: tag relations with relationship meta-objects (way IDs in database-world); tag physical attributes to geospatial objects (earth coords in a way). --Hamish 15:33, 30 April 2010 (UTC)

A multipolygon doesn't model a relationship, is is simply an improvised area element - and tags that apply to the area represented by a multipolygon should go to the relation by definition. Removing redundant tags from multipolygon members is good practice, and strictly speaking not doing so even leads to wrong results. (The outer way explicitly can represent a feature in its own right, so it would be correct, albeit not advised for a robust renderer, to view it as a second lake without a hole overlapping the multipolygon lake). I will remove the remark if there are no objections. --Tordanik 18:14, 8 December 2012 (UTC)

Water were bathing/swimming is forbidden

See Talk:Bathing#Water were bathing/swimming is forbidden --Olejorgenb 23:14, 11 July 2011 (BST)

Water sub-areas

There are often parts of waterways/lakes/reservoirs with different properties (whitewater, watersport permission/usability). Whitewater sports treats some of them as linear features with optional area element delimited by riverbanks ([[1]]) but for a more elaborate model it would be required to have lakes/rivers divided into many arbitrary water areas. Would that work with natural=water? Or should there be one water area delimited by the shore which is overlapped by areas defining access etc? RicoZ (talk) 11:27, 11 September 2015 (UTC)

these subparts are not delimting water by itself. You can just draw another object completely covered by the water area, and add the necessary tags. For example a boundary for a natural reserve on part of a lake, or an object representing a sport activity, a marina, a dangerous/restricted area, you don't need to split the water area, but don't place any additional water=* tag on these parts (if you do it, you'll have to split the water=* area into several parts, but this will be often wrong as you'll have to duplicate other tags for naming for example the same lake when there's only one lake, even if there's some physical delimitation on the surface such as a raw of buoys). — Verdy_p (talk) 13:10, 12 March 2016 (UTC)

Question about level=-1 / underground

Is ist apropriate to tag a underground water canal with natural=water? For example:

In theory yes - if you really use level and not layer. In practice many tools may have trouble with it. We have underground canal's that can be represented with waterway=canal+tunnel=yes + one of layer=-1,location=underground, level=-1. However the "tunnel" is essential and so far there is no area representation of a tunnel. man_made=tunnel has been proposed but did not get far although I would endorse it.
One workaround is to use covered=yes instead of tunnel, it is legal, can be applied to natural=water and if tools don't support it please complain in the bugtrackers:) RicoZ (talk) 19:33, 28 December 2018 (UTC)
The level=* key is intended for indoor mapping of buildings, so in my opinion it's not appropriate to use it on an underground canal. A satisfactory solution will likely have to involve area representations of tunnels – covered=yes doesn't really express that the feature is underground. --Tordanik 20:19, 14 January 2019 (UTC)
covered=yes doesn't say it is underground but that may not be really necessary - it should suffice to know it is covered by other features/areas. At least if it is covered by man made objects the case should be pretty obvious? RicoZ (talk) 21:27, 14 January 2019 (UTC)
It matters with 3d rendering, for example, where you want to dig through the virtual ground in one case (tunnel) but not the other (covered). Not super-important, as it can always be improved later, and sadly there is no perfect solution available yet. But as a 3d enthusiast, I felt like adding my two cents. :) --Tordanik 22:06, 15 January 2019 (UTC)
Not sure if I understand you correctly. Tunnels should be through "natural" ground although I am not sure it is documented anywhere. Covered features may be even above natural ground. Arguably location=underground could be added though I would promote Proposed features/man made=tunnel for those that are truly underground. There is also something in the middle of it - complex urban areas where the natural is way bellow apparent ground. I am wondering if some kind of level model should be adopted for such cases?
For 3D mapping I would think use of key:ele would help many things.RicoZ (talk) 20:33, 22 January 2019 (UTC)