[OSM-talk] Large Rivers in general, mapnik rendering in Particular

[Andy Allan]

On Feb 8, 2008 11:09 AM, Artem Pavlenko <artem.mapnik at googlemail.com> wrote:

> We can make osm2pgsql or coastline tools to create polygons, but why
> not create them in the first place ?
> Can someone enlighten me, please ?

If I wanted to draw the rivers as light blue* with dark blue
riverbanks, wouldn't storing them as polygons would make this hard? I
don't think it would be easy to work out which sections of the
polygons are where the river continues as opposed to being the
riverbank.

If we store the riverbanks, then we can pre-process to our hearts
content using osm2pgsql and the like. That way I could have riverbanks
as polylines and rivers as polygons and render them as I see fit. The
pre-processing could work very similarly to the coastlines, using a
left- or right-hand side rule and continuing the riverbank where one
way joins onto the next to construct the polygons required.

Cheers,
Andy

* As I think more and more about contours, and semi-transparent
renderings and so on I realise that most area-fills will be
translucent with edges on my maps, so we need to avoid abutting
polygons if we aren't intending to represent an edge.