Coastline

From OpenStreetMap Wiki
Jump to: navigation, search
Available languages — Coastline
· Afrikaans · Alemannisch · aragonés · asturianu · azərbaycanca · Bahasa Indonesia · Bahasa Melayu · Bân-lâm-gú · Basa Jawa · Baso Minangkabau · bosanski · brezhoneg · català · čeština · dansk · Deutsch · eesti · English · español · Esperanto · estremeñu · euskara · français · Frysk · Gaeilge · Gàidhlig · galego · Hausa · hrvatski · Igbo · interlingua · Interlingue · isiXhosa · isiZulu · íslenska · italiano · Kiswahili · Kreyòl ayisyen · kréyòl gwadloupéyen · Kurdî · latviešu · Lëtzebuergesch · lietuvių · magyar · Malagasy · Malti · Nederlands · Nedersaksies · norsk bokmål · norsk nynorsk · occitan · Oromoo · oʻzbekcha/ўзбекча · Plattdüütsch · polski · português · português do Brasil · română · shqip · slovenčina · slovenščina · Soomaaliga · suomi · svenska · Tiếng Việt · Türkçe · Vahcuengh · vèneto · Wolof · Yorùbá · Zazaki · српски / srpski · беларуская · български · қазақша · македонски · монгол · русский · тоҷикӣ · українська · Ελληνικά · Հայերեն · ქართული · नेपाली · मराठी · हिन्दी · অসমীয়া · বাংলা · ਪੰਜਾਬੀ · ગુજરાતી · ଓଡ଼ିଆ · தமிழ் · తెలుగు · ಕನ್ನಡ · മലയാളം · සිංහල · ไทย · မြန်မာဘာသာ · ລາວ · ភាសាខ្មែរ · ⵜⴰⵎⴰⵣⵉⵖⵜ · አማርኛ · 한국어 · 日本語 · 中文(简体)‎ · 吴语 · 粵語 · 中文(繁體)‎ · ייִדיש · עברית · اردو · العربية · پښتو · سنڌي · فارسی · ދިވެހިބަސް
Logo. Feature : Coastline
One example for Feature : Coastline
Description
Where the land meets the sea
Group

Marine

Tags

natural=coastline

The coastline is a rich and complex environment at the edge of the marine environment including cliffs, beaches, harbours, headlands, bays, wetlands and islands.

Tagging coastlines in OSM

The natural=coastline tag is used to mark the Wikipedia-16px.png Mean high water spring which is the point of the highest tide. See natural=coastline for all the details. See also de:Coastline for much more details.

Using OSM coastline data

The presentation of the coastline is often more complex than that for other features and there can be delays between changes being made to the high water line and its appearance on the map.

The main problem of showing coastlines from OSM data is that many renderers really need closed polygons. The polygon can (and normally should) be made of several ways, but the ways should join end-to-end and eventually loop back round without interruption, to close the polygon. An imperfect coastline with many small gaps, reversed ways and other defects will cause the polygon to break, and the coastline to be rendered incorrectly . One of the features of the Coastline error checker is to try and join coastlines in such a way as to make high-quality coastlines even with these imperfections. As the coastlines are uploaded and completed the quality can be checked.

Rendering in Standard tile layer on openstreetmap.org

At low zoom levels (used for z0-9), up to and including zoom level 9, Standard tile layer renders all the sea as a solid fill of blue, generated from the shapefile simplified-land-polygons-complete-3857.zip, which has a relatively low resolution. At higher zoom levels the coast polygons used are generated from a larger shapefile (land-polygons-split-3857.zip). These files are automatically generated daily from planet dumps + diffs, but they will only be made available if the coastlines are geometrically correct (or can be fixed to be correct, so no intersections etc.) and if they are not too different from the last valid coastline.

Coastline rendering in Standard tile layer on openstreetmap.org may update later than other rendering changes. There are two reasons for this:

  • To avoid major disruptions of map rendering due to data errors (entire continents displayed as sea instead as land) the coastline is not automatically updated if there are larger changes in the geometry compared to the last time it was successfully processed. For example any addition or removal of a large lake with coastline tag will require manual intervention. You can look at the update times of the layers on http://openstreetmapdata.com/data/land-polygons to see when the last successfull update of the coastlines was done.
  • Normally changes in OSM data will be detected by the update process on the tile servers and affected tiles will be marked as to be updated. This does not always happen correctly for coastlines. The problem is that the need for the update might be detected and a re-rendering scheduled, but if at that time the new coastlines aren't available (see above), it will re-render the old coastlines. So sometimes it needs further changes to trigger the re-render again.

See also