[OSM-talk] Mapping canals

[Gervase Markham]

Stephen Gower wrote:
>   Hi Gerv - I've snipped lots below - if I haven't commented on any
>   part, I pretty much agree.
> 
> On Mon, Jan 21, 2008 at 06:36:48PM +0000, Gervase Markham wrote:
>> Narrow sections are denoted by maxwidth. One narrowboat (just over 7 
>> feet) is given as 2.5m. Two boats is 5m. It's not necessary to mark a 
>> two-boat width restriction for bridge holes, which are implied narrow.
> 
>   I don't mind there being an assumption that unspecified units are
>   metres, but the UK canals are done in feet, and if I'm going to put
>   any dimensions in, it'll be in feet, so I'd need a way to specify
>   that's what I'd done.

Richard seems to have chimed in with superior knowledge here, so I'll 
defer to him. Apparently we can use non-metres if we specify.

>> "boat=private" is used for private parts of the canal.
> 
>   I see no reason not to use access=private, myself, since the
>   towpath can have a seperate access tag.

OK... I picked this up because it's defined on the Map Features page. 
But maybe best practice has moved on since then?

>> The "lock=yes" way(s) takes various lock-related information, including:
>>
>> - the lock name, if it has one, with "name=<foo>".
> 
>   since this way is also part of the waterway, name= is already in
>   use for the name of the waterway - we need something else for the
>   lock names.

Good point. Does this problem have analogies with other sorts of way? 
How is it dealt with there?

>> A flight of locks with a unifying name (e.g. "Hatton Locks") is denoted 
>> with a node placed in an appropriately central position with new tag 
>> value "place=lock_flight" and "name=<name>".
> 
>   Better to group them with a relation, I'd have thought.

You may be right. I'm not too up on relations. <reads>

>> Mooring info should be attached to the relevant stretch of towpath [...]
> 
>   On UK canals, mooring is generally allowed everywhere, except where
>   explicity signed otherwise 

This is true. But there is also a need to mark places where mooring is 
explicitly provided for or encouraged. (I'm sure you'd agree.)

> - do we need a tag for
>   mooring-not-allowed?

I think we do. Would it be reasonable to have "mooring=yes" meaning 
"there is explicit mooring here", "mooring=no" meaning "you may not 
moor", and nothing being "well, it's the bank, knock yourself out"? Or 
would that be confusing, given that most other yes/no tags are dual 
state rather than tri-state?

Gerv