[Tagging] tagging city gates and sally ports

[Martin Koppenhoefer]

I recently noticed that there is already a description for
historic=city_gate in the wiki:

http://wiki.openstreetmap.org/wiki/Tag:historic%3Dcity_gate

Current description reads: "A city gate (or town gate) is a gate
within a city wall."

which is not bad, but should IMHO be amended. City gates are often
objects that continue to exist also when the wall has been demolished,
be it physically or in a more abstract form (very often there are
place names refering to city gates, they are often recognizable in the
city structure/layout even when partly or completely demolished).

There is also a wikipedia link from the above page that has a better
definition of it: http://en.wikipedia.org/wiki/City_gate  (because
refers also to situations with removed walls).

I would like to extend the city gate definition also to spots where
there is no actual gate anymore. Recently I stumbled upon these. In
one example there is no gate any more, but some remains of the walls
are still present (as base for later built buildings atop of them),
there is still a street there which enters into the old town and the
local people still refer to the place with the name "foo gate".

My suggestion is to use historic=city_gate on all places where there
is or was a city gate (possibly together with "name" and additional
information like WP links, historic:civilization, etc.), and to add
additional tags for situations with actually in place gates or
structures. If there is a gate that is closed I'd use
barrier=city_gate and building=city_gate, if there is only an arch
(empty opening) but no gate I'd add building=city_gate but no barrier
tag (dependent on the situation and prior mapping you might also add
barrier=entrance in some situations).

On the above page there is also the suggestion to tag these as
barrier=sally_port which is so poorly defined in OSM and wikipedia
that I am not sure what the actual meaning in OSM is (mainly because
there seems to be a problem with the interlanguage links: the German
version of sally port describes a lateral gate used for attacks in
times of siege (de:Ausfalltor) while the English version seems to
describe a security lock (not the small one with keys but a system of
rooms used to controll access) (de:Sicherheitsschleuse)). The German
version is refering to what is described in the English section of
"Etymology and historical usage". IMHO there is no benefit in tagging
these 2 different features with the same tag, just because in English
language there is these 2 usage applications in different contexts.

What do you think? Can we clarifiy the two tags?

cheers,
Martin