OpenStreetMap Coastline Errors

This map shows various errors in ways which are tagged as natural=coastline in the OpenStreetMap database.

“Error points” layer
These are places where the coastline does not form a continuous series of ways; either because of a gap or because a way is drawn in the wrong direction. These errors will almost always lead to rendering errors. This layer is generally updated daily, last updated on: 18 March, 2013 .

“Bad Geometry” layer
Most usualy this marks a location where there is a self-intersecting coastline way, but other problems are also identified. Clicking the marker brings up a popup with the description of the problem.

“Lake Points” layer
These are not geometry issues but tagging issues. This layer identifies closed ways (or a series of ways) which are within the main landmass and tagged as coastline. For larger water bodies this is currently probably the best method of tagging, but this is not the case for smaller water bodies, and the points identified are usually therefore a tagging error. The two most common instances are (i) small water bodies tagged as “natural = coastline” instead of “natural = water”, or (ii) islands in lakes which frequently get tagged as “natural = coastline” rather than making these islands an inner way of a multipolygon relation.

“Missing Shape Parts” layer
These issues are likely to occur very infrequently. The only noted instances occurred where the corner of a coastline tile just crosses the coastine. If the coastline way intersects the tile, but there is no node within the tile, then bad geometry is created in the shapefile.

Creation of the data for these last three layers requires more manual processing and so they are updated less frequently, last updated on: 18 March, 2013 .

Credits:
Map generated by D Groom using files produced by P Norman using code written by Martijn van Oosterhout
“Bad Geometry” and “missing shape parts” layers generated using additional code by Michal Migurski