Render implied oneways (roundabout, motorway, motorway_link)

[sommerluk]

Some tags imply oneway=yes. This PR renders them as if oneway=yes would be present. (Condition: There is no oneway=no present.)

junction=roundabout
highway=motorway
highway=motorway_link

This resolves #467

Are there any other tags that imply oneway=yes?

[pnorman]

if turning this into a multi-line CASE then have each WHEN on its own line

[matkoniecz]

List of tags is consistent with https://github.com/openstreetmap/iD/blob/master/js/id/core/oneway_tags.js and not contradicted by wiki http://wiki.openstreetmap.org/wiki/Key:oneway#Implied_oneway_restriction

[matkoniecz]

But is contradicted by http://wiki.openstreetmap.org/wiki/Tag:highway%3Dmotorway_link#Tagging_oneway "Most motorway_link roads will be one way, and should be tagged oneway=yes. Any unusual motorway link road which is two-way should be explicitly tagged oneway=no.". Added in http://wiki.openstreetmap.org/w/index.php?title=Tag:highway%3Dmotorway_link&diff=929508&oldid=917617

[sommerluk]

"Most motorway_link roads will be one way, and should be tagged oneway=yes. Any unusual motorway link road which is two-way should be explicitly tagged oneway=no."

This seems to requiere always a oneway=* tag (either “yes” or “no” or “-1”). But for me, this sentence seems to make no assert on the default value.

On the other side, the ValueDescription box on the wiki page lists oneway=yes in the section “Implies”.

How should we proceed?

[dieterdreist]

2015-03-12 14:44 GMT+01:00 Lukas Sommer notifications@github.com:

"Most motorway_link roads will be one way, and should be tagged
oneway=yes. Any unusual motorway link road which is two-way should be
explicitly tagged oneway=no."

This seems to requiere always a oneway=* tag (either “yes” or “no” or
“-1”). But for me, this sentence seems to make no assert on the default
value.

On the other side, the ValueDescription box on the wiki page lists
oneway=yes in the section “Implies”.

How should we proceed?

IMHO there is no such implication for oneway=yes. Have a look at actual
tagging, 94% of all motorway_links have an additional tag oneway=yes, if
this was an automatic implication, mappers won't add this tag. In
preliminary mapping, motorways often get mapped as one way rather than
mapping 2 oneway carriageways (OK, this is preliminary, and maybe we're
over this phase for most parts of the world).

[matthijsmelissen]

98% of the motorways and 99% of the motorway links have a oneway tag. So I don't think adding implicit oneway=yes arrows is useful here.

27% of the roundabouts has a oneway tag. In this case, adding the arrows might be useful.

[sommerluk]

Okay. I propose to close this PR and open a new PR only for roundabouts.

What should I do with the indent for the “END AS oneway,” line?

[sommerluk]

Closing in favor of #1367