[mkgmap-dev] Coastline issues - analysis and possible solution

Mon Aug 29 17:08:44 BST 2011

> First, you will have to download and process much more data than just
> the country extract.

This is why I shared my extracted coastlines. The extraction has to be 
done only once. Everyone else can just download the (relatively small) 
coastline files.

> Second, if the continent extract was generated at a different time than
> the country extract and there have been edits to the coastline, your map
> might not correspond to any snapshot of the OSM database.

Absolutely. What I uploaded yesterday were snapshots based on the most 
recent Geofabrik Europe extract and the most recent full planet. If 
these prove useful, I will make the generation a batch job so that the 
coastlines updated whenever a new Geofabrik Europe extract or full 
planet are made.

> Right, the idea is to make the combined bounding box of the
> splitter-generated tiles something else than a rectangle. If we ensure
> that all coastlines that were "cut open" in the Geofabrik extract will
> have their endpoints outside the splitter-generated coastline, the
> flooding should be gone.

There is no need to make the combined bounds non-rectangular. The 
simplest solution actually is a rectangle, one large enough to cover all 
splitter-generated tiles plus the padding added to these by boundary 
rounding.

> I wonder if Geofabrik or some other entity could start providing a
> little wider coastline extracts that are in sync with the Geofabrik
> country extracts.

This is exactly what I volunteered to do. The wider regions I would 
extract coastlines for are Geofabrik Europe (daily) and planet (weekly). 
We have the server capacity and are happy to do it. Our website is not 
set up for it yet but I can use my private hosting for now. I am trying 
to gauge interest. If people are interested in such regular extracts, I 
will be happy to provide them.

> Boundary extracts could be nice too, but I suppose that the Geofabrik
> country extracts already include all the boundary=administrative
> lines of the country.

This is an interesting point. The boundary files seem to be updated 
about once a month right now. If there is interest in such boundary 
extracts, I could see what I can do on our servers.

- Bartosz