[OSM-dev] coastline polygons

[Martijn van Oosterhout]

On 2/13/07, Frederik Ramm <frederik at remote.org> wrote:
> What is the number of nodes required to map every street, track, and
> path in the whole word? (Which is our ultimate goal, isn't it?)
> Compared to that, I assume that the coastline is peanuts. It may look
> a lot at the moment because our database only covers a tiny fraction
> of existing roads, but in the long run it is negligible.

No, the coastline is going to be many more points for sometime to
come. The estimate is around 1.6 million kilometres of shoreline
worldwide. If you're going to put a point every 20 metres you get 80
million points. You get that many segments and a smaller number of
ways.

Comparing with roads is not a good comparison, roads are straight and
tend to not use many points. Coastlines OTOH are never straight. More
accurately, coastlines have a fractal dimension, they cannot be
described in a finite number of points. The more you zoom in, the more
points you need.

> Plus, coastline changes all the time, see Japan or Dubai. While many
> of these changes will probybly go unnoticed at the moment, it is very
> likely that at some future point in time if they create a new "World
> Island" somewhere, an OSM contributor will follow the project closely
> and enter the new islands as they are created. *If* given the chance.

Sure, it's nice to be able to do that. But on the other hand there are
hundreds of thousands of kilometres of coastline in Greenland, Norway,
etc what no-one is ever going to check. It's going to be done by
computer algorithm from satellite photos.

However, my reason for seperating the data is something else: I would
like the maps on openstreetmap to be just a layer in a more
comprehensive system. Say we had a layer that gave altitudes. It would
be nice to put that under the normal maps so you could make an atlas.
By insisting everything go into OSM you've cut that off. We need to
make room for alternate data sources, and that means not storing all
the data in OSM to start with.

Have a nice day,
-- 
Martijn van Oosterhout <kleptog at gmail.com> http://svana.org/kleptog/