Proposed features/natural=cave

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Map the inside and extents of caves
Status: Draft (under way)
Proposed by: RicoZ
Tagging: natural=cave
Applies to: area,way
Definition: Cave extents and objects/features inside caves
Drafted on:
Proposed on: 2016-06-14

Map the approximate extents of caves and objects inside them similar to Proposed features/man_made=tunnel.

natural=cave can be an area representing the approximate extent of a cave or a linear way in cases where the exact form of the cave is not known sufficiently well to map it or a mix of both methods can be used.

Objects and ways inside caves should be tagged in a similar way as Proposed_features/Simplify_man_made=bridge_mapping#Objects_on_bridges.

The cave relation can be used to share common attributes, collect parts and relate objects which are known to belong to a particular cave but where exact connection can not be mapped.

How to map

This is about mapping the interior of caves and ways and objects inside them. If you want to map a single cave icon use natural=cave_entrance.

The cave

Caves can be mapped as ways or areas depending on their shape and how much information is available.

  • as area: draw the area, tag it with natural=cave
  • as way: draw the way, tag it with natural=cave. For caves consisting of many linear ways it may be a good idea to add area=no to minimize the risk of confusion.
  • combination of both methods, as above it may be a good idea to use area=* to minimize the risk of confusion.

natural=cave have an implicit location underground and don't need a layer tag unless they cross other underground objects.

Where caves or their branches cross at different depths (no connection) they should have different layer=* values or alternatively could be distinguished by ele=*.

Points and ways inside or parts of caves can have ele=* values where known.

Fee and access conditions may be attached to a natural=cave_entrance or to the relation if used.

Avoid nodes of type natural=cave as there are plenty of them in the database and widespread confusion what they mean.

Ways, objects and natural features inside the cave

Ways (such as highways, waterways) in caves:

  • for linear caves add the appropriate tags to the way representing the cave, resulting for example in a way tagged with natural=cave+highway=path
  • for area caves draw the way through the cave, tag it and add location=cave and the same layer (if any) as the natural=cave

Objects in caves such as POIs, benches, waste baskets:

  • node type objects which are part of one of the ways of the cave or inside the cave or the outline declared by natural=cave are considered to be part of/inside the cave and inherit the layer attributes of those ways (if any) - no additional tagging is needed.
  • other objects (ways or points not part of the way natural=cave) will be considered to be inside/part of the cave if
    • they are within the area defined by the natural=cave and
    • have the same layer as the cave and and
    • are tagged with location=cave

Sometimes large cave domes can have ways or other objects crossing at different levels, those should be differentiated with level=*

Cave relation

A relation can be used to

  • group together caves consisting of more parts
  • assign name and other common attributes valid for several parts of a cave
  • map various features inside caves

Some mappers prefer to use cave:ref instead of a relation to group together elements of a cave.

Key Value Discussion
type cave
name a name Cave name
fee yes/no fee
access * common access values
operator operator name who is running the cave

Members

Area outline zero or more a way forming the outline of a cave section, those may be tagged with natural=cave additionally
Way linear zero or more a linear way representing a cave section, those may be tagged with natural=cave additionally
Node Way Area inside zero or more ways,POIs and other objects inside the cave. Those should be additionally tagged with location=cave and layer as described above.
Node Area entrance zero or more objects of type natural=cave_entrance

Other tags

See cave for fee, access etc.

Possibly natural=* + location=cave could be used to map the "landscape" within the cave.

Sinkholes are often parts of cave systems: natural=sinkhole

Data consumers

Data consumers should ensure that ways tagged with location=cave or natural=cave are handled in a similar way like ways tagged with tunnel=yes.

Routers should observe that objects in caves are reachable only by ways tagged with location=cave or natural=cave.

Specialized renderers may render the natural=cave in a way similar to that of Proposed features/man_made=tunnel. For linear segments a tunnel like rendering could be adopted.

Data validators/error checkers:

  • should tolerate that natural=cave may be both linear or areas
  • should tolerate highways, waterways and railways with an additional natural=cave and/or location=cave
  • should tolerate type=cave for relations
  • should understand that both natural=cave and location=cave imply underground location
  • may check for errors in use of area=*
  • may warn about natural=cave nodes (many should be cave_entrance)
  • may check that highways/railways are entering the cave through natural=cave_entrance or (manmade) tunnels (no such strict requirement for waterways)

Examples

Situation before proposal