[Tagging] Subway vs light rail

[Fernando Trebien]

A German mapper just changed the rail type of a line [1] in my area
(southern Brazil) from light_rail to subway.

Here those trains run on the surface (contrary to most subways) and
have no at-grade intersections with other traffic (contrary to most
light rail systems). Also, metro systems like this are usually
considered "heavy rail," [2] so it really doesn't look like this
should be "light rail". It is also not simply railway=rail since it is
not the highest level of rail service and it only carries passengers.

Grade separation seems to be the main distinguishing criteria as per
what's written in the wiki [3][4][5]. Do you think we could clarify on
the wiki that there may exist subway systems that run entirely on the
surface?

[1] http://www.openstreetmap.org/relation/420335
[2] https://en.wikipedia.org/wiki/Light_rail
[3] https://wiki.openstreetmap.org/wiki/Key:railway
[4] https://wiki.openstreetmap.org/wiki/Tag:railway%3Dlight_rail
[5] https://wiki.openstreetmap.org/wiki/Tag:railway%3Dsubway

-- 
Fernando Trebien
+55 (51) 9962-5409

"Nullius in verba."