I have an interest in abandoned/derelict canals (and the existing ones too!).
I note that there is extensive mapping of derelict canals but there doesn’t appear to be any way to get them to render.
Perhaps I’m missing something, or it’s an oversight in OSM.
Can somebody please advise?
Many thanks…
All renderers choose what to display and what not. Most however choose to not render historical objects with little to no visual appearance remaining, because OSM is mainly intended for today’s maps.
If you like, you can take a look at OpenHistoricalMap.org. It’s the go-to place for historical objects and natively renders them (within their time period). Note that it is much less populated compared to OSM and licensing is different, so you can’t just copy things from OSM to OHM.
If there are traces left of old canals (potentially non-continuous), then those can be mapped within OSM of course.
There is also a currently on-going project to map the Ludwig Canal (LDMK): Ludwig-Donau-Main-Kanal (Alter Kanal, Ludwigskanal). Perhaps it can help you too.
Thank you for replying quickly.
It’s a fair point about not displaying historical canal lines on current mapping. As you suggest sections that still hold water, for example, can be mapped as discrete areas and tagged accordingly. I have seen examples of this.
There is a related problem however. There are many significant remaining structures for example locks and aqueducts. These are mapped in OSM and associated with the canal which has the derelict tag. This prevents these structures of historical significance from being rendered.
I suggest that this is incorrect. By way of comparison here in the UK Ordnance Survey maps show sections of derelict canals that contain water and structures of significance which are often of interest to visitors to the area.
My next question then is how to tag such structures in OSM so that they render as discrete objects.
I had a quick look at the thread about the Ludwig Canal and translated it from German to English. It is more difficult to understand as a result but I will take a further look when I have more time.
We call this “tagging for the renderer” and it is discouraged. The better course of action would be to make a pull request on your favorite project that renders OSM data so these features show up. Note however that no map will ever show everything and different maps will choose to show different things.
Thank you, that’s useful advice. I’m still learning…
By pull request do you mean suggesting to OsmAnd, for instance, that they render such features?
Different maps show different things. There are 6 different map styles visible at OpenStreetMap.org but all of them only show a tiny fraction of the data in OpenStreetMap itself. You’re mapping in the UK and Ireland; if you want a map that shows historic and derelict canals in OSM have a look at one of mine.
That said, the challenge with canals is that something that “used to be a canal but isn’t any more” can cover a whole range from “nothing left on the ground at all” through to “a big ditch with water in it, but not usable for navigation for technical reasons such as the locks no longer work”.
Whether the former belongs in OSM is essentially the same question as is asked about dismantled and razed railways (see topics in this forum and elsewhere too numerous to mention). Most are probably tagged waterway=derelict_canal but something still obviously a canal but not navigable I’d probably map as waterway=canal; disused=yes.
A “pull request” is basically “some code that you’ve written that changes the way that something works so that it does what you want” that you suggest should be included in some project.
The challenge with doing this with OsmAnd is that OsmAnd’s rendering rules are spectacularly complicated; doing this with OsmAnd’s offline maps would require a lot of time just to get familiar with how they work.
However, I think that it should be possible to use those map tiles of mine as an online background map in OsmAnd. I did that when I used to use OsmAnd, and currently use those map tiles as a background in Vespucci - see here.
I would add that if canal left behind clear remnants it is possible to map this detail.
For example water areas, wetlands and more are mappable and will be commonly rendered.
Are those mapped and currently hidden?
Oftentimes it is difficult to make general recommendations. Especially considering that every map chooses what it wants to show; Changing tagging solely for the purpose of getting it to render a certain way is frowned upon.
If you have a certain canal in mind that could use some restructuring, you might want to open a thread like the guys did for the LDMK. This way, you can get in contact with others who are also interested in the area.
Thank you for your guidance.
Bizarrely the link you offer is to the exact stretch of canal I’d been looking at (as part of the Newport Branch of the Shroppie).
That section, along with the rest of the branch is tagged as derelict_canal which prevents the rendering of features such as the aqueduct at Longdon-upon-Tern.
Tagging waterway=canal; disused=yes when a section holds water, for example, will I presume render the canal but it then would I think appear as navigable being indistinguishable from navigable lengths on the main network which aren’t tagged as disused=yes. (Though a bit of common sense would make it clear that such disused sections are disconnected.)
What I think is the desired outcome is what I mentioned earlier, the Ordnance Survey approach. They show sections in water as continuous blue channel, dry identifiable sections as a channel with dashed lines. Significant features appear in both scenarios.
Looking at your very helpful Useful Maps you will see what I mean about the aqueduct… it doesn’t appear. However the rendition of the dashed line channel is an useful addition (though I think the very pale blue shading is hard to see on certain backgrounds).
Thanks for the explanation. I won’t be going down that route.
How might your map tiles be used as an overlay in OsmAnd?
There appears only to be the option to add predefined backgrounds from an extensive list.
Thank you.
Yes, I’ve seen that done on some disconnected bits of derelict canals.
The structures don’t get rendered it seems if the tag waterway=derelict_canal is used.
I’ve got the message about changing tagging to force rendering. The examples shown in the link are awful!
It’s more that there isn’t a tag that the map renders.
I had a look at this (former) canal: OpenStreetMap
It seems to me that most of it is filled in, without leaving traces. Those parts will likely never be shown on general maps. They are historical and belong in OpenHistoricalMap.
But there are some parts that aren’t and those are interesting. I could find some visible water areas, which you can tag with
natural=water
water=canal
This way, the water-filled sections will show up.
There are also some locks, I imagine, though I don’t know where they are. If they are still there and can be visited, you can make nodes there and tag them like this one: OpenStreetMap
If the dry sections have some walls still visible or other features, then you can map those too and they will likely be rendered.
In short, it can take some time to correctly tag the canal. It’s not as easy as just changing some tag for a way that in reality just doesn’t exist in that form.
Well, sort-of. The aqueduct doesn’t appear because that map has never been told how to show derelict canal aqueducts. Compare with, say, this canal aqueduct. The glib thing to say here is “pull requests welcome” which means “it’s not a priority for me to add that to the map style, but I’d be happy if someone else did that”.
However, in OpenStreetMap there are usually two sorts of bridge rendering. There’s the fact that “this feature goes over a bridge” (in that M65 example, three different features do), and then there’s the bridge itself, which can be mapped as man_made=bridge. Here is a railway example not far to the south.
I haven’t done it for ages, but this old help question may still work, specifically the “example URL http://map.atownsend.org.uk/hot/{0}/{1}/{2}.png” bit.
Thank you. That’s a stretch of canal I’ve been considering.
I realise that each feature needs to be treated separately.
That works fine apart from the opacity slider having no effect. The layer has to be switched on and off.
Thanks…
(The blue is definitely too pale.)
It’s designed as a base layer rather than an overlay - sounds like you want an overlay of “former canal features” rather than a map 
. That’s not that difficult to do, but I don’t know if one exists.
Thanks Andy. I shall be using the overlay as is, it will be very helpful.
I assume you’re aware of OpenCanalMap? The ability to superimpose on old OS maps is very useful.
Thanks for your guidance. I’m a beginner at all this but finding it very absorbing. I travel throughout the year in my motorhome in the UK and also Europe, so I will be contributing very frequently.
