Hi. It's nice to see the Water Cover page anticipate a tagging question :) Just looking at wikipedia, they say that beaches need to be formed by gradual deposit of solids from dissolved in waves, which means (a) rocky shorelines might not be a beach, and (b) definition of beach is confusing enough that "rocky surface covered by tidal water" is a nice neat unambiguous description of the feature.
Whether anything renders it is another matter... ;) [1] http://en.wikipedia.org/wiki/Beach#Beach_formation On Mon, Apr 14, 2008 at 4:51 PM, Steve Hill <[EMAIL PROTECTED]> wrote: > On Mon, 14 Apr 2008, Chris Hill wrote: > > > High and low water marks vary every day, the height of the tides vary a > > lot.. > > Correct - anyone who records high and low watermarks on maps/charts will > be using the highest and lowest astronomical tides, not the high/low tide > of an arbitrary day. > > > Most measurements are made using Mean Sea Level, which > > doesn't change (rising sea levels aside). > > The options are generally to record lowest, highest or mean watermarks. > ISTR that Ordnance Survey mark all three on their Explorer maps don't > they? And maritime charts rarely (never?) bother with mean - they are > marked up in heights above/below lowest astronomical tide. > > > When you look at the Yahoo > > images, how do you know what state the tide is? > > You don't (other than being able to guestimate based on local knowledge). > However, in some locations the coast line data is quite inaccurate and can > be approximated by hand based on local knowledge and the Yahoo images. > Some of the beaches around here (Gower, South Wales) are very flat and the > very large tidal range of the Bristol Channel means the distance between > high and low water marks can be over a kilometer. > > At the moment, nothing states what natural=coastline is actually supposed > to be documenting, so when estimating the coastline by hand you have no > idea whether to put it at the top of the beach, at the bottom of the beach > or somewhere in the middle. > > I'm not expecting to be able to record the coastline with a huge amount of > accuracy, but even an estimate is more accurate than the (big) distance > between high/low water marks in some locations so defining what we are > recording is important. > > - Steve > xmpp:[EMAIL PROTECTED] <[EMAIL PROTECTED]> > sip:[EMAIL PROTECTED] <[EMAIL PROTECTED]> http://www.nexusuk.org/ > > Servatis a periculum, servatis a maleficum - Whisper, Evanescence > > > _______________________________________________ > talk mailing list > talk@openstreetmap.org > http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk >
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