For many year now I have been running a service at <a openstreetmapdata.com, first alone and then with the help of Christoph Hormann. We offered processed OSM data for download, most importantly coastline and Antarctic icesheet data. And although the service was always free to use and the software mostly Open Source, this was always our show. For a long time I wanted to change this and turn this into a proper OSM community project, and, finally, we have taken a big step towards that.

Three years ago I launched the OpenStreetMapData.com [Update: Discontinued June 2019, some data now available from osmdata.openstreetmap.de]. web site to host the OSM coastline data extracts I was generating. Since then I have been updating those extracts at least daily and offering them for download on that site. The coastline extracts are used in many OSM maps including the OSM standard style.

I have written before about my work on the software doing the assembly, repair, and conversion of the OSM coastline data. I wrote the Osmcoastline software and I run it daily to create shapefiles with land and water polygons available for download on OpenStreetMapData.com [Update: Discontinued June 2019, now available from osmdata.openstreetmap.de]. For a while this data has now been used on the main OSM map. Unlike with the old process, this new process usually makes sure the map is updated within a few days when the coastline changes.

A year ago I released the first version of the OSMCoastline program that extracts and assembles coastlines from OSM data. Since then I have learned more about coastlines in OSM than I ever wanted to know, fixed numerous coastline bugs myself and added more features to the software. OSMCoastline has been in production use at Geofabrik and the German map server for more six months now.

I have written before about the mapping of Antarctia in OSM. Since then there has been a lot of activity. Christoph Hormann has prepared better Antarctica data for import and has documented the planned import extensively on the wiki. Peter Körner has created a web map in Polar Stereographic Projection.

OpenStreetMap wants to map the whole world, but there is a whole continent that has been neglected a bit: Antarctica. Of course there isn’t much there besides rocks, ice, and penguins and not too many people live there. But still, it is a huge area and it should appear properly on our maps.

In the last months I have spent a lot of my spare time working on the OSMCoastline program mentioned several times in this blog already. It is by no means perfect yet, but it works and several people have tried it and used its output. But it is not the easiest program to use with all its options and you need a current planet file to work from, not everybody has one lying around. So I thought about how to make access to its output easier for everybody.

For a while now I have been working on OSMCoastline adding features bit by bit. (See this blog article for some background info.) OSMCoastline now closes small gaps in the coastline and it can split up the huge polygons into smaller ones. You can create land polygons or water polygons depending on your needs and you can have it all in WGS84 or in the usual Mercator projection used for tiles web maps (EPSG 3857). So it does a lot more than the coastcheck application used for these things before. And the software is still a lot faster.

Every map of the world has to take into account that there are land areas and water areas. You could have huge polygons for each continent and paint them on a blue background. But handling those huge polygons is difficult. OpenStreetMap solves this problem by having ways tagged with “natural=coastline” and the convention that the land is always on the left side of this way. So a continent or an island is surrounded by one or more ways in counter-clockwise order. It is much easier to edit those coastlines instead of large multipolygon relations or something like it. Coastlines are the only case where OSM has this special rule.