[Tagging] Streets as footways in Venice, Italy

[Fernando Trebien]

On Tue, Feb 26, 2019 at 3:23 PM Sergio Manzi <smz at smz.it> wrote:
> And in Venice there is an official designation of roads accordingly to their availability in case of exceptional high tides ("Acqua alta") of different heights, but AFAIK this essential information is not registered anywhere in OSM...

Even though it is not so comparable, in Brazil we have some places
with really narrow public access paths that we decided to tag
differently and we have so far liked the result (see [1] for an
example). The criteria is simply if the way is wide enough for a car,
if it's not then it gets downgraded to footway. This situation happens
somewhat often in Venice too and it can be verified simply by
measuring the distance between buildings using JOSM's measuring tool.

For instance, I quickly found this street which is 1.5 m wide, too
narrow for a car: https://www.openstreetmap.org/way/24990562

In some other cases, the measuring tool can also be used over imagery,
such as to measure the widths of ways along channels, like this one,
which is 1.8 m wide: https://www.openstreetmap.org/way/175023361

Also, wide ways that are only accessible through narrow streets would
also be downgraded to footway, like this one:
https://www.openstreetmap.org/way/216498689

The wiki says that highway=pedestrian [2] is meant for streets in
which some vehicle traffic may be authorized. I don't think this is
the case of most places in Venice (all my searches turned up that no
vehicles, not even bicycles, are authorized there). The Italian
translation of this article reflects this idea on the second
paragraph. So I think that many highway=pedestrian in Venice are
indeed incorrectly tagged and should be highway=footway.

I would propose that highway=pedestrian is used there to represent the
safe, wide paths used during acqua alta and that others that may be
submerged (even wide ones that may still be tagged as
highway=pedestrian) receive tidal=yes, even if the adoption if this
idea is low [3][4]. Acqua alta is indeed more common in a season, so
seasonal=yes/winter is a possibility as well.

It would be nice to have highway=* with tidal=yes or seasonal=yes
rendered differently, but there are no open tickets asking for that
yet [5]. Of the four tags that may be used to indicate intermittently
submerged highways (tidal=*, seasonal=*, intermittent=*, ford=*), only
two are often combined with highway=* (ford=* and seasonal=*). As
ford=* is for a different use case, I think it would make sense to
request that seasonal=* highways get rendered differently.

If all that makes sense and you do decide to classify Venice's streets
differently, then I would recommend that the Italian wiki pages for
highway=footway and highway=pedestrian contain a note about it, to
avoid confusion among mappers. Also, link from those wiki pages to a
forum thread discussing the topic in Italian, so as to help build
consensus and for verifiability.

Regards,

[1] https://www.openstreetmap.org/?mlat=-30.10559&mlon=-51.24465#map=18/-30.10559/-51.24465
[2] https://wiki.openstreetmap.org/wiki/Tag:highway=pedestrian
[3] https://wiki.openstreetmap.org/wiki/Proposed_features/Tidal_road
[4] https://wiki.openstreetmap.org/wiki/Proposed_features/Tidal_path
[5] https://github.com/gravitystorm/openstreetmap-carto/issues

-- 
Fernando Trebien