[OSM-talk] Mean high water level rendering

[Ed Loach]

Borbus wrote:

> I have recently been mapping tidal areas where data for both mean
> high
> water and low water levels are available.  I have drawn the MHW
> level
> and tagged it as natural=water, natural=riverbank or
> natural=coastline.
>  Then I have drawn natural=beach, natural=mud, natural=land,
> natural=wetland etc. up to the MLW level.
> 
> For example see: http://osm.org/go/0EZaXWxC-
> 
> First question is does this seem a reasonable way to map MHW and
> MLW?
> If so I think I will start a wiki page on how to do it.

natural=coastline should be used for MHW as per the wiki [1]. 

For the area between MHW and MLW I have used multipolygons for
either natural=wetland/wetland=tidalflat or natural=beach/tidal=yes
(both of which can be seen here:
http://osm.org/go/0EH53Vkp--
)

I adopted this method I think from copying how someone had mapped a
similar area further along the coast, but forget the details now.

Your example seems to be a little more inland than the example I
quoted so things may need mapping a bit differently, but the tidal
areas I've looked at near here reach up the River Colne as far as
Colchester and the River Stour to the sluice at the A137 crossing.
There is a trac ticket to make tidalflat's look a bit better when
the background is sea rather than land in Mapnik [2]. Osmarender
doesn't seem to handle the complexity of the multipolygons (turning
most of Harwich into a beach, for example).

Ed

[1] http://wiki.openstreetmap.org/wiki/Tag:natural%3Dcoastline
[2] http://trac.openstreetmap.org/ticket/1607