# Aqueduct or Tunnel or both

A discussion about how an aqueduct crossing a highway should be mapped has arisen. IMO it’s obvious that an aqueduct should be mapped as it is in nature. Yet this collides with the rule bridges should be avoided across tunnels.

An aqueduct is a rather distinct object and has most of the time its own name. Besides a highway passing under an aqueduct doesn’t get its name. Even when you pass under an aqueduct you notice the aqueduct. Mapping a tunnel under an aqueduct doesn’t make much sense, since one never gets the impression of moving into and out of a tunnel.

To see what’s happens when a waterway (no aqueduct) crosses above a highway (tunnel) is mapped go to https://www.openstreetmap.org/#map=18/53.18479/5.81920.
Other better samples:
https://www.openstreetmap.org/#map=19/51.98960/4.32345
https://www.openstreetmap.org/#map=19/51.97200/4.60222
https://www.openstreetmap.org/#map=19/53.05679/5.84104
IMO the best solution is to map the waterway an aqueduct (layer=0) and the highway as an underpass (layer=-1). I’n not opposing mapping the highway as a tunnel (layer=-1). So the rule avoid bridges across tunnels wouldn’t apply here.

First example on Mapillaryto get an impression what wyo is talking about

I agree you should not map both tunnel and bridge in this example. But it’s a close call if bridge or tunnel would be better. I’d say both would be ok and I wouldn’t make a big fuss about it.

In the Dutch forum no consensus was reached about a proposal to tag aqueducts as bridges with man_made=bridge and bridge=yes.

This is an example of a more bridge-like aqueduct. The middle bridge is an aqueduct.

Indeed. So for the moment we tag them in accordance with the OpenStreetMap convention of not tagging both tunnel and bridge (aqueduct in this case); something we have reached consensus on.

The aqueducts concerned are all of the type where a tunnel was dug under an existing waterway (such as the M.C. Escher Akwadukt, the Margaretha Zelle Akwadukt, and the Akwadukt van Harinxmakanaal), and where the tunnel walls are vertical. While the tunnel/bridge distinction can be very subjective, in the case of these aqueducts you wouldn’t even know you were sailing/swimming/kayaking over one unless you consulted a map.

A bridge bridges. One can clearly see the bridge part in all examples.

A tunnel is dug out, one can see clearly the sub-level sidewalls and the road going downward. Dugout tunnels are sometimes covered with a man made roof.

maybe ‘make’ a key ‘landcover’ + define all ‘things’ about it , and then landcover=aquaduct or landcover=water + water=aquaduct + layer=* or maybe better natural=water + water=aquaduct + layer=* ?

I disagree with that. A tunnel is not dug out but through something. If the above way needs a supporting construction than it is a bridge.

You probably don’t drive on water else you wouldn’t say this. Aqueducts are many times smaller than the cannel and the shoreline is made of concrete. If I know that’s an aqueduct ahead I avoid passing other ships on the aqueduct. Besides aqueducts are sightseeing objects. IMO it’s essential to see aqueducts on the map.

The tunnel/bridge distinction is subjective yet definitely not in these cases. As I said before aqueducts are noticed quite well even from the under passing highway while one gets not the slightest impression of a tunnel. Therefore aqueducts are also landmarks on the highway as are other bridges, crossing, etc.

Why do you insist on the rule “avoid bridges across tunnels”? Aqueduct maps correctly the waterway and tunnel maps the highway going below surface. Both have their rights. IMO the rule doesn’t make sense in this case.

It is important for aqueducts used for sailing to appear on a map rendering intended for inland waterway sailors, but in terms of OSM, the map is underlying database, not a rendering of it. The default rendering on the web site is intended as an aid to mappers, not as an end user map, and has to be selective in what it renders, to avoid excessive clutter in highly mapped areas.

Did you ever pass any of the three aqueducts I mentioned? The canal does not become more narrow, and the banks only hint at recent construction.

I don’t, the community does. It’s a strong OpenStreetMap convention. If you do double tag bridges/tunnels, other mappers will eventually remove one of them. If you wish to address that, start a discussion on the tagging-mailinglist, because it has a lot of consequences.

If you want aqueducts to be tagged as bridges everywhere, you’ll also have to stop OpenStreetMap-carto from rendering them with an outline, because it causes really wacky rendering — currently a blue ‘bridge’ lying in the middle of a wide water-area, not visibly connected to anything, because the canal routing lines have the same colour as the canal’s water area. Again, if you don’t other mappers will likely remove the bridge-tag at some point, even if that means breaking the ‘don’t map for the renderer’ rule.

These are pictures of two aqueducts near Akkrum and Grou. I think this shows clearly that aqueducts are correctly mapped.

We always map objects as they are and never as they were rendered nicely. It’s up to the programmers of a renderer to show objects nicely but never up to the mapper.

There are two types of tunnels:

• a tunnel that goes underneath something, f.e. a river,
• a tunnel that goes through something, f.e. a mountain.

There is only one type of bridge from that perspective:

• a bridge that bridges a gap.

Starting with a tunnel always works, so that is ambigious. Starting with a bridge solves the problem.

Good day,

I am a cycle traveller and actually don´t have too much time to waste for specific problems. But mapping is my new hobby and I want to do it as correct as possible. I thought it is a fun thing to do, mapping things along my way, but I am crawling deeper and deeper down the rabbit hole and slowly it becomes too much. A specific example I found in Zacatecas City, Mexico, I came across an old aqueduct. It wasn´t tagged right. I read through countless articles, OSMwiki, forums but still I am not smarter than before.

https://www.openstreetmap.org/edit#map=18/22.76867/-102.57528

I followed all rules, you can check the tag. But it is not rendered in OSMand, which is my reference. The bridge-tag should not be used, for it is historic. However, I checked other aqueducts, e.g. the Ferreres Aqueduct (https://www.openstreetmap.org/edit#map=18/41.14522/1.24496), which is tagged as bridge, although historic and the mapper tagged the whole thing as a ditch. Super weird, but it shows in the map of OSMand.

Community, I know, this topic is highly controverse, but please give me an idea, how to map that god damn aqueduct.
I played around with layers too, giving the aquaduct the layer value 1 and the streets, three in total, -1. Did not work, the streets still go over the aqueduct. Then I read, that I can leave the streets at 0 and just give the aqueduct the value 1. However, all this does not matter, once I delete the bridge tag, it does not appear at all. I guess, this is a rendering problem.

Also, the aqueduct kinda crosses houses. I can´t really verify what is going on there and if I should adjust the shape of the properties/houses too.

I have one more day, in which I can use a computer. After that I am on the road again. I hope, someone has a smart idea what I can do here.

Greetz, Erlendur

I think I might have found the issue. In the wiki entry about OSMand (https://wiki.openstreetmap.org/wiki/OsmAnd) under supported POI, under historic, aqueduct is NOT listed. Therefore it is NOT rendered, is my conclusion. I did a test with historic=monument, which it is too, the result is, that it is still not rendered, BUT at one end of the aqueduct a monument symbol appears with the name. Once clicked on it, the outlines of the aqueduct appear. However, this isn´t really helpful. The monument node sits at the Southern end, somewhere over the houses.

As one member mentioned above, we mappers should map things as they are, not how they look best on a map. The latter is the matter of the renderer of the different application, right. Therefore my last idea is the following:
I tag it as historic=aqueduct, I leave away the monument tag, but give it a name tag. This results in an invisible aqueduct, at least in OSMand. But additionally I place a monument node close to, where most people see the aqueduct and name it. Therefore it would be tagged correctly, the aqueduct as historic, although not displayed in OSMand, but the single node showing a tourist or traveller, that there is something intersting, would work in OSMand.

As for the layers, I still have the aqueduct as layer=1 but I went back to layer=0 for the streets. In Openstreetmap this results now in the streets going over the aqueduct. I still don´t understand why. If someone thinks, layer=-1 for the short section of road, which actually runs under the aqueduct, please tell me. I can change it. However, I can´t check if that works, for as I mentioned, it is not rendered in OSMand and earlier, with the bridge tag, it did not work. Only in OSM I can see it.

I am still open for suggestions. I know, that it should be tagged histori=aqueduct. Please advise me, if I should leave it like that.

Cheers, Erlendur