[OSM-talk] the coastline

[Richard Weait]

On Mon, Mar 21, 2011 at 5:45 PM, Robin Paulson <robin.paulson at gmail.com> wrote:
> i've recently been doing some mapping around auckland, adding coastal
> walkways. one in particular i walked on sunday has two routes: one at
> the foot of the cliffs, one on the road at the top of the cliffs. the
> lower route is under water when the tide is in, so walkers are advised
> to follow the road route.
>
> so, i added the route, and it is now under water:
> http://www.openstreetmap.org/?lat=-36.927322&lon=174.709115&zoom=18&layers=M
>
> this seems wrong, drawing a route which is then under water, but the
> alternative of moving the path is also wrong.
>
> so, what do we do?
>
> the question becomes (in my mind): why do we have a single way mapped
> 'coastline'? this implies the boundary between land and water is
> static, but of course it moves - a number of times per day.
>
> i like the possibility of a high water mark and a low water mark, used
> together to entirely replace the natural=coastline tag.
>
> perhaps some of you have some ideas around this also?

I don't have a solution but I certainly admire the problem.

To complicate things, while maps may show mean high-water, borders
seem to be mean low-water. WIkipedia says so.  Adjusting a coastline
polygon based on aerial imagery will get us something in between.  Or
something not-between because mean high-water is a mean.  So that's
all really bad and difficult to map.

How about extending intermittent=yes from rivers and streams to
footways as well?  It would take an advanced router to know to look
for intermittent=yes to avoid that path for the walker less likely to
check conditions for themselves.

Perhaps highway:intermittent=footway  so that the intermittent footway
fails to be found by tools that aren't aware footways can be
intermittent?