[OSM-talk] Mapping canals

[Richard Fairhurst]

Gregory wrote:

> I think there is someone on OSM who lives on a canal boat, or does  
> quite a bit of canal boating. I seem to remember them providing  
> some input into discussions, but can't remember who they are.

That'd be me. :) I live on a boat half the week, my day-job is editor  
of Waterways World magazine, and I've worked for British Waterways  
(their www.waterscape.com website) in the past. And I draw a lot of  
canal maps for the magazine!

Berto d' Sera (who has a userpage on the wiki) has also expressed  
some interest.


Gervase Markham wrote:

...a lot of good stuff, so I'll spare you the "me too"s. A few  
comments that might be helpful:

> - waterway=lock_gate might be great for the Manchester Ship Canal,
> doesn't work so well for narrowboat canals. Locks are 70ft long or  
> less,
> and marking the upper and lower gates individually seems  
> unnecessary and
> makes them harder to render. Locks also have names (e.g. "Hatton  
> Bottom
> Lock") which seems to make them better rendered with nodes.
>
> On the other hand, canals have no direction of water flow (with a  
> couple
> of exceptions) but locks are directional. So one might want to  
> indicate
> that by using a short directional way. (But should the way point  
> low to
> high or high to low?) Or perhaps level tags either side of the  
> lock, but
> that could interact badly with bridges if this persisted along the
> canal. (I'd expect the entire canal to have "level=-1" to make  
> creating
> bridges over it easier.) One might also consider "ele" either side,  
> but
> accurate data is hard to obtain with a GPS. Is there best practice in
> this area?

I agree that there should be the option of mapping a lock with a  
single node.

Direction can be solved simply by making the way of the canal point  
"downstream" (though there's generally no water flow as such, the  
locks are generally all in the same direction either side of the  
summit level). The Trent & Mersey Canal, for example, heads uphill  
west from the Trent as far as Stoke-on-Trent; it then passes under  
Harecastle Hill in a tunnel; and then continues downhill towards the  
Mersey. 73 locks in all, but just two directions.

For bridges: level=-1 could cause problems with aqueducts. Suggest  
bridges are just level=1 as per usual and the canal, without a level  
tag, is therefore an assumed level=0.

> [some good points snipped]
> - It is useful to denote the rise/fall of a lock (again, universally
> measured in feet). There needs to be a tag for this. We could
> appropriate "depth", but it's not actually the depth of the canal.

"rise" is the standard term.

> - waterway=aqueduct should surely be applicable to ways rather than  
> nodes?

Should be both: an aqueduct can be as long as Pontcysyllte, crossing  
an entire river valley, or just a simple culvert-style construction  
over a stream.

> - All canals have towpaths. These paths are of varying quality, and  
> this
> information is useful to walkers and cyclists. The towpath can be on
> either side. How should the towpath be denoted? As a separate way
> parallel to the canal? What tags should be used?
> ("highway=footway,bicycle=yes")? How should quality be denoted?

Towpaths are generally, but not always, permissive paths where the  
landowner is (for a UK canal) British Waterways. Yes, it should be a  
separate way. Cycling is permitted on some, but not others, so this  
too needs to be expressly tagged.

As for quality, this is a wider need - decent tags for expressing the  
surface of a way and what types of bike it's suitable for.

> - Tunnels often have rules about who can enter and when (e.g. transit
> north beginning between :00 and :15; south between 30: and :45). We  
> have
> "hour_on" and "hour_off" - is that enough? How should such tags be
> applied, given that the restrictions are different in each direction?

I think there's a proposed relation on the wiki which might address  
this.

> - There are "mile markers" along the canal which are useful for
> navigation and as points of reference and interest.

Just nodes, for which we need a tag, I guess. Exactly the same as the  
mileposts that you used to find on UK roads, that you've always found  
on French roads, and that are being introduced on UK motorways and  
some principal roads as well.

cheers
Richard