Symbols for locks on canals

So far mapnik displays a filled circle and osmarender a black chevron “>” for locks in zoom level 15-18. Since most people don’t use so small levels this should be extended to at least level 12-14. Also I’d like to suggest another rendering if possible.

On level 12-14 a crossing line in the same color as the canal should be shown. It should be 3-5 times as long as the canal width. Since most canals are just single lines this is sufficient to show locks yet won’t introduce too large symbols.

On level 15-18 it should be a chevron (angle 150°, black color) pointing agaist the water flow. The size should be the same for all levels about as wide as on the upper levels but never smaller than the canal width. This means if a canal is wider the chevron it as to be enlarged to fit the width.

For locks tagged as single point this is sufficent. Locks tagged as a waterway with 2 points, on level 12-14 only the one gate (upper?) should be displayed. On level 15-18 both gates should be displayed yet without connecting side lines as osmarender currently does.

Even if locks are only interesting for tourists and ship drivers, IMO they would increase the usability of the maps.


I’d broadly concur with the above with the following difference:-

The connecting lines for multiple single lock gates should be retained as in the instance of a staircase where the locks are not separate i.e. the upper gates of one lock are the lower gates of the next. With the joining lines this would then conform to the normal way of depicting a staircase. These staircases cannot be mapped as waterway=lock because of this sharing of gates.

All normal locks should be always be mapped as waterway=lock and single lock gates should only be used in special cases. If a lock is marked with two chevrons, it would suggest two locks not one. (My opinion.)

I have actually used OSM for navigating the canals and waterways of the UK on a narrowboat and will be doing so again in September. (I use Tangogps on an Asus EeePC 701)

The name “single lock gates” is missleading since it implies a single gate without any high difference. Yet that’s not a lock but just a gate (movable damm).

In the case of a staircase where some gates are for upper and lower chamber of water, they belong together into a single lock even if it has multiple water chambers. IMO these should be tagged as a single waterway=lock with more than 2 gates. There’s no restriction to have multiple gates in a lock yet there’s always an upper and a lower ending gate. There are several different type of locks (e.g. normal 2-gate lock, staircase, inclined plane, elevator, etc). A tag “lock_type” would made sense for any special type.

In level 12-14 locks should only give a overview that a canal has locks. Even rather long staircases should be markt with a single symbol as I proposed before (small crossing line). Level 15-18 should be more detailed, therefore each gate of a lock should be shown with a symbol (chevron against water flow). Below level 18 locks may not be shown with a symbol but only if drawn as a multipoligon area, even if just some interesting locks were drawn.

IMO it doesn’t make sence to have different symbols for different types of locks. In the case of a staircase showing each gate without connecting lines are sufficient. Different symbols won’t give additional information while just complicating drawing.


Okay, I’ve tought again about the connecting lines between gates. I agree it would make sence to see which gates belong together. Yet IMO 2 black connection lines would make lock symbols too prominent against other symbols on the map. I’d suggest a single dotted black line in the middle of the waterway. This should be enough to show which gates belong together while not making lock symbols standing out. Also it would make it easier to render locks like .


I must say that I prefer the joining lines for a staircase, it’s what I am used to. The example you give does look terrible but in my opinion it should not be tagged as a lock, it should have it’s own tag and matching symbol.

Well it is a lock, no matter how it looks like, albeit a special case. Unfortunatly one can’t have a symbol for each case. So it’s much better to have a single symbol which fits all or at least most cases. This certainly will be a requirement if locks where accepted for rendering in Mapnik.


I believe that there are technical reasons why Mapnik cannot yet display symbols that change with the orientation of the way. It’s a known issue and I’m sure it’ll be resolved. There’s no need for you to talk about it much more or to start wiki pages. If you can code the Mapnik developers might appreciate your help though. :slight_smile:

I’ve just look into the bug tickets and yes the technical issue is resolved albeit not released. Yet that’s not what I think is sensible displaying locks, the choosen symbol looks more like a highway sign pointing towards a direction. Also it’s only visible in level 16 and below which means it doesn’t have to be drawn altogether.


Richard is correct.