[Tagging] units and notations for depth

Tony Shield tony.shield999 at gmail.com
Tue Feb 19 11:18:16 UTC 2019


Quite right. For OSM purposes I suggest depth in metres, if water is 
tidal=yes also tidal_range in metres.

I can't think of any reason to try to replicate nautical charts and tide 
tables. And when planning navigation I do not consider not using formal 
navigation charts and tables specific to that purpose.

TonyS


On 19/02/2019 10:56, Colin Smale wrote:
>
> On 2019-02-19 11:11, Tony Shield wrote:
>
>> Depth of water in tidal areas can vary enormously. People using depth 
>> for navigation and general use would expect to use depth at MLWS 
>> (Mean Low Water Springs) and add increments based on tide tables, I 
>> suggest that OSM does the same. Use the tidal tag and perhaps a 
>> tidal-range tag, in metres, tidal_range is the difference between 
>> MHWS (Mean High Water Springs) and MLWS.
>>
>> note - Spring tides are the highest and lowest forecast tides and are 
>> based on the relative position of the earth, moon and sun.
>>
> Indeed, they are astronomical predictions, but not forecasts. They are 
> not in themselves good enough for planning a (route to a) berth in a 
> harbour for example. There are many other factors influencing the 
> actual water level, like global/local weather conditions and seiche 
> waves. Depth is of course also affected by dredging operations...
>
> Should OSM aim to replicate the Admiralty Charts and tide tables?
>
>
>
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