Re: [OSM-talk] Rocky beaches
On Monday 14 April 2008 13:46:34 Steve Hill wrote: I'm attempting to trace some of the Gower coastline from the (very fuzzy) Yahoo images. But I'm not sure how to tag beaches made up of flat rock. For example, the type of thing shown by this Google aerial view: http://maps.google.co.uk/maps?f=qhl=engeocode=jsv=107ie=UTF8ll=51.5615 98,-4.302907spn=0.003855,0.015836t=hz=16 And photograph of the same location: http://www.nexusuk.org/photos/other/gower/2006/04/15/img_3465/view I don't really want to tag it with just natural=beach since that would imply a sandy/shingle beach (i.e. something nice for bathing on), but I can't really see an appropriate tag. From the proposal at http://wiki.openstreetmap.org/index.php/Proposed_features/Water_cover it seems that natural=beach, surface=rocky (or surface=rock?) and optional water=tidal tag if you feel like it :) Regards, Matt Williams signature.asc Description: This is a digitally signed message part. ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] Rocky beaches
natural=scree perhaps? http://wiki.openstreetmap.org/index.php/Key:natural http://en.wikipedia.org/wiki/Scree Stefan On Mon, Apr 14, 2008 at 2:46 PM, Steve Hill [EMAIL PROTECTED] wrote: I'm attempting to trace some of the Gower coastline from the (very fuzzy) Yahoo images. But I'm not sure how to tag beaches made up of flat rock. For example, the type of thing shown by this Google aerial view: http://maps.google.co.uk/maps?f=qhl=engeocode=jsv=107ie=UTF8ll=51.561598,-4.302907spn=0.003855,0.015836t=hz=16 And photograph of the same location: http://www.nexusuk.org/photos/other/gower/2006/04/15/img_3465/view I don't really want to tag it with just natural=beach since that would imply a sandy/shingle beach (i.e. something nice for bathing on), but I can't really see an appropriate tag. - Steve xmpp:[EMAIL PROTECTED] sip:[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 ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] Rocky beaches
On Mon, 14 Apr 2008, Stefan Baebler wrote: natural=scree perhaps? Scree refers to steep slopes covered with loose stones - this is (very uneven) horizontal solid rock. - Steve xmpp:[EMAIL PROTECTED] sip:[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
Re: [OSM-talk] Rocky beaches
On Mon, 14 Apr 2008, Matt Williams wrote: From the proposal at http://wiki.openstreetmap.org/index.php/Proposed_features/Water_cover it seems that natural=beach, surface=rocky (or surface=rock?) and optional water=tidal tag if you feel like it :) Excellent - that seems to be a good answer, thanks. Although I note that the proposal doesn't mention whether it should also be tagged as natural=beach (how do we actually define a beach? It's rather a vague idea). I've also raised a question on the natural=coastline talk page about what the coastline actually denotes - I can't see anything saying whether it is the high water or low water line (I'd assume it's the low water line - i.e. everything to the right of it is always sea, no matter what the state of the tide, whilst stuff to the left of it is assumed to be land (tagged as water=tidal if it is flooded at high tide). - Steve xmpp:[EMAIL PROTECTED] sip:[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
Re: [OSM-talk] Rocky beaches
On Monday 14 April 2008 15:46:14 you wrote: On Mon, 14 Apr 2008, Matt Williams wrote: From the proposal at http://wiki.openstreetmap.org/index.php/Proposed_features/Water_cover it seems that natural=beach, surface=rocky (or surface=rock?) and optional water=tidal tag if you feel like it :) Excellent - that seems to be a good answer, thanks. Although I note that the proposal doesn't mention whether it should also be tagged as natural=beach (how do we actually define a beach? It's rather a vague idea). I know, it's a rather incomplete proposal but surface=rock seems a sensible way to tag it. Personally, I wouldn't actually call that rocky peninsular a beach so I agree on the fuzzyness. I've also raised a question on the natural=coastline talk page about what the coastline actually denotes - I can't see anything saying whether it is the high water or low water line (I'd assume it's the low water line - i.e. everything to the right of it is always sea, no matter what the state of the tide, whilst stuff to the left of it is assumed to be land (tagged as water=tidal if it is flooded at high tide). I'd agree with your assessment here. Otherwise, perhaps a natural=coastline with a tide=high or tide=low tag and then essentially have two coastline shapes for beach areas. Though perhaps this would be hellish for the renderers? Matt Williams signature.asc Description: This is a digitally signed message part. ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] Rocky beaches
High and low water marks vary every day, the height of the tides vary a lot.. Tidal ranges in the south west of England can be about 13 metres in height. Most measurements are made using Mean Sea Level, which doesn't change (rising sea levels aside). When you look at the Yahoo images, how do you know what state the tide is? cheers, Chris Steve Hill wrote: I've also raised a question on the natural=coastline talk page about what the coastline actually denotes - I can't see anything saying whether it is the high water or low water line (I'd assume it's the low water line - i.e. everything to the right of it is always sea, no matter what the state of the tide, whilst stuff to the left of it is assumed to be land (tagged as water=tidal if it is flooded at high tide). ___ Yahoo! For Good helps you make a difference http://uk.promotions.yahoo.com/forgood/ ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] Rocky beaches
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] sip:[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
Re: [OSM-talk] Rocky beaches
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 ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] Rocky beaches
Lots of coastline in OSM comes from PGS data. According to http://wiki.openstreetmap.org/index.php/PGS_whitepaper This new shoreline is an approximation of the High Water Line; it is NOT a Mean High Water Line since the source data have not been tide coordinated. This of course says nothing about other coastline data. Dutch topographic maps don't consider tidal flats a part of the land. It is coloured the same colour blue as the sea, but it has lots of black dots in it. -- m.v.g., Cartinus ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] Rocky beaches
Also, if you are in an area with extensive coastal swamps (mangroves for example) be aware that the PGS data usually traces the land side of the swamp. This makes sense, looking at the statement below, but the mangrove swamps can extend for many kilometres to sea, and I wouldn't want to sail through them. Stephen On 15/04/2008, Cartinus [EMAIL PROTECTED] wrote: Lots of coastline in OSM comes from PGS data. According to http://wiki.openstreetmap.org/index.php/PGS_whitepaper This new shoreline is an approximation of the High Water Line; it is NOT a Mean High Water Line since the source data have not been tide coordinated. This of course says nothing about other coastline data. Dutch topographic maps don't consider tidal flats a part of the land. It is coloured the same colour blue as the sea, but it has lots of black dots in it. -- m.v.g., Cartinus ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
