Tag:natural=coastline

+/- natural=coastline Description Used to mark a coastline. Used on these elements Useful combination Used combinations in World Australia/Oceania Europe (list) Asia (list) Central America (list) South America (list) Africa (list) Status Undefined

Please see also Coastline, and much more specific: de:Coastline

The following Coastline tag was accepted onto the Map Features page.

Key	Value	Element	Comment	Example
natural	coastline		A way drawn along the coastline; this should ideally be positioned at the average high tide line. Direction should be such that land is on the left side and water on the right side of the way.

Contents 1 How to use 1.1 Unbroken interlinked ways 1.2 Direction 1.3 Overlaps 1.4 Tidal position 1.5 Coastline becoming a river 2 Renderer usage 3 Discussion 4 See Also

How to use

Draw a way along the coastline.

Unbroken interlinked ways

One long way can be drawn around the perimeter of an island, to loop back on itself (an area ). However for larger landmasses (most coastline) it is not practical to trace the entire coastline as one way. Instead we can arrange the ways end to end (and typically limit the length of any one way to no more than ~500 nodes).

Note that the ends must meet to form a continuous interlinked coastline. Some renderers/tools also require the ways to form a complete polygon (eventually looping back on itself). For Europe you can use OSM Inspector coastline debug view, to check that the coast line is correct.

Direction

Equally important for rendering. The direction of the way should be chosen such that land is on the left side and water on the right side of the way (when viewing in the direction of the way arrows). If you regard this as tracing around an area of land, then the coastline way should be running anti-clockwise. Obviously this applies to all the ways forming the complete coastline polygon, such that one way ends on the same node where another way starts. It's easy enough to reverse the direction of a way in Potlatch, JOSM, and all good editors.

Overlaps

Do not cross a coastline over itself - this has no meaning and may cause renderers to behave badly. Don't use the same point twice (pinch point) other than the start/end point (if appropriate). If you want to make an island, start a new way.

Tidal position

The coastline way should be positioned at Mean High Water Spring (MHWS), the "average high tide" line. And in non-tidal waters (tide less then 30 cm) at Mean Sea Level (MSL).

Realistically speaking the vast majority of our natural=coastline ways will be based on PGS data for a long time to come, and some will be corrected based on Bing or Yahoo Aerial Imagery (variable tide level), but if you get the opportunity to fix up the data while out surveying, then the high tide position is the one to go for.

If you are interested in mapping other tidal positions, take a look at Proposed features/Water cover

Coastline becoming a river

There is an ongoing discussion about how we should tag the coastline as it goes into an estuary and becomes a river. See Proposed features/Tidal Rivers

Renderer usage

This data is used by the main renderes Mapnik, Tiles@home, more detailed technicalities can be read Coastline.

Discussion

Do this at Talk:Tag:natural=coastline. Also read the mailing list posts linked above

See Also

• Tag:natural=wetland
• Tag:waterway=riverbank
• Key:coastline:survey_quality
• natural=water is for inland lakes, and should not be used for tagging ocean coastline. Equally natural=coastline should not be applied to the edges of a lake. FIXME: even if it's a really huge lake? (see discussion)
• Key:waterway may list some useful related features.