Talk:Coastline

Contents 1 Closed Polygons 2 Note on Coastline and Yahoo imagery 3 Failure to render 4 Translation 5 Tagging Low water 6 Proposed Merge of Page

Closed Polygons

It says "Mapnik really needs closed polygons", but is that realistic? I mean are we really going to try to draw a single closed way around the entire coastline of Asia for example?

I thought it was widely agreed that we would not do that. A single way made up of many thousands, probably millions, of nodes, will cause problems for the various softwares, and for the OSM Protocol interface itself. I remember a discussion related to long motorways in the US, where it was agreed that they should actually be chopped into smaller ways if they get beyond a certain length, just to make the data easier to swallow.

Also it seems a rather fragile requirement. Would the Mapnik coastline rendering of the Netherlands suddenly break, if somebody disconnected the polygon over in India?

The tiles@home approach Tiles@home/Dev/Interim Coastline Support is a bit hacky (which I guess is why it's described as an interim solution) ...but it works, without the need for closed polygons.

-- Harry Wood 16:04, 27 November 2007 (UTC)

There doesn't need to be a single way in the OSM database in order to derive a complete polygon. As long as the adjacent ways share a common node then the shapefile can be created from the adjacent ways. As an example see the coastline of Hawaii, which exists as many ways in the OSM database, but from which a shapefile has been created for the Mapnik coastline. Dmgroom 19:09, 27 November 2007 (UTC)

Aha. Yeah it ocurred to me afterwards that might be what was meant. So a "closed polygon" doesn't mean a single closed way.

There's still a problem of it being fragile. And if Mapnik derives a polygon, does that mean it's loading in all of the ways? e.g. encircling the whole of Asia. It's a lot of data to shunt around, just to render the blue on the right side of a line. -- Harry Wood 15:06, 28 November 2007 (UTC)

Note on Coastline and Yahoo imagery

The Coastline of Conakry (Guinea) is interesting 'cause they have high differences in tides (see http://www.mobilegeographics.com:81/calendar/year/1333.html). It can be up to 3 meters - so the yahoo image was taken on low tide. --katpatuka 08:35, 8 February 2008 (UTC)

Failure to render

Sometimes I have modified the coastline and added some land features as well, and while the land features show up, the coastline is updated at far zoom levels but remains the same at near zoom. What is happening here? CrystalWalrein 13:04, 5 March 2009 (UTC)

• can you give an example Dmgroom 13:38, 6 March 2009 (UTC)

Here is an example. Osmarender has already accepted the coastline, but Mapnik does not, even when Metacarta Up-To-Date is used. CrystalWalrein 23:14, 6 March 2009 (UTC)

• I've got the same problem after editing St-Laurence river (Montréal - canada) with potlatch/yahoo!. Osmarender accepted the coastline I had edited but Mapnik does not. Example. Something new about editing coastline and get the proper picture ? Daniel 04:28, 9 june 2009 (UTC)

• Here is an other example, even the coastline checker does not work propperly. Any explanation for this? --Noframe 14:10, 13 June 2009 (UTC)

• The coastline error checker is currently experiencing issues with the server. . Dmgroom 11:18, 16 June 2009 (UTC)

• Thanks for your Information! --Noframe 14:33, 16 June 2009 (UTC)

So is the renderer actively buggy, or just slow? Eg. [1] here I did some major changes to the coastline of Bintan Island, and while nearby roads etc already show up on the rendered map, the coastline is still the incorrect old version. Jpatokal 13:22, 25 September 2009 (UTC)

Just slow I think. It says on the page, the shapefiles are generated "every few weeks" -- Harry Wood 14:12, 25 September 2009 (UTC)

• Another example. I edited the northern portion of Harstine Island to reflect the sat imagery, and after a few week it still hasn't updated.--Emesscgs 04:11, 4 July 2011 (BST)

Translation

The German page de:Coastline is much more specific. Please translate it to English. Thanks, --Markus 14:05, 5 September 2009 (UTC)

Tagging Low water

Are there any established methods of tagging the low water? PeterIto 22:24, 17 March 2012 (UTC)

There is this proposal Proposed_features/Water_cover, which is not a direct answer to your question, but obviously one edge of any tidal area would be the low tide mark. Dmgroom 19:27, 18 March 2012 (UTC)

Thanks, however that does seem to be stuck and to an extent taken over by wetland. On reflection I guess wetland does everything that is needed, and is already being used in some places. All it needs is some more clarity on how to tag sand, or 'beach' that gets covered at high tide and one is done. I will look more carefully at wetland. PeterIto 21:50, 18 March 2012 (UTC)

Proposed Merge of Page

I am proposing to merge this page with natural=coastline which contains essentially the same information. At present mappers need to look at both pages to get all the detials of how to map coastline, and how it renders.Dmgroom 12:49, 7 May 2012 (BST)

Yeah the two pages have been around for a long time. Maybe the separation originally was to do with coastline rendering details (and all the quirks) going on the "Coastline" page. Elsewhere on the wiki we do have this idea of "Feature" pages vs tag documentation. e.g. we have Railways in addition to Key:railway. See also Wiki organisation. Feature pages are a sort of general guide mentioning many tags, while tag documentation is supposed to give more brief structured info. So we could change it to better follow that kind of idea, but yes at the moment Coastline and Tag:natural=coastline have ended up having very similar info. -- Harry Wood 04:23, 8 May 2012 (BST)

Point taken, maybe just a bit more of a tidy up of the two pages is all that is needed. Dmgroom 11:38, 8 May 2012 (BST)

Thanks Harry/ Dmgroom. I have just given the coastline tag article a bit of a cleanup into simpler headings prompted by the above. Please make sure I have got it right, but I would suggest that we then add any more details about coastline to this article. The Whole subject of beaches, mud flats etc need some more work. Also how to map low-water. Could I also alert people to a discussion taking place on talk:Harbour which relates in a way to the coastline and where some additional views and input could be helpful. PeterIto 12:10, 8 May 2012 (BST)