[OSM-newbies] motorway _link and _junction tagging

[Phil! Gold]

* Alan Mintz <Alan_Mintz+OSM at Earthlink.Net> [2010-04-20 19:10 -0700]:
> Onramps:
> - name: "<motorway name> <direction> onramp" e.g. "CA-210 West onramp"

Hm.  That's not a bad idea.  "onramp" and "offramp" seem cluttered to me,
but I can't come up with anything I think works better.

> - ref: "from <street>[ <direction>]" e.g. "from Rosemead Blvd North". 

Isn't ref usually used as some sort of numbered identifier?  I'd think
that ref should either be the exit number or nothing.  In theory, the
"from" information is implied by the road the ramo is connected to.

> Exit node (where offramp joins motorway):
> - name: "<street>[ <direction>][ <other name>]" e.g. "Azusa Ave North - San 
> Gabriel Canyon". The name as official/signed.

I've also been putting in the destinations listed on the sign, so an exit
onto I-95 might read "name=I-95 North; Baltimore; New York".

> - ref: "Exit <exit number>" e.g. "Exit 23A".

I usually just have the number, so I'd use "23A".  I think the "Exit" is
implied.

> Exit ramp:
> - name: "<name:exit_node> offramp" e.g. "Azusa Ave North - San Gabriel 
> Canyon offramp". Take the name tag's value from the related Exit node and 
> add " offramp".
> - ref: "<ref:exit_node> from <motorway> <direction>" e.g. "Exit 23A from 
> I-10 East"

What do you do in cases where multiple ramps merge before meeting the
destination road?

I haven't been putting motorway_junctions at the end of ramps because most
of the mentions of them on the wiki (not to mention the Mapnik rendering
for the slippy map) seem to treat them as just for departures from a
motorway, not entrances.

> Final thoughts:
> 
> With motorway interchanges (with other motorways), I treat the connectors 
> as onramps - the <street> role being the originating motorway and the 
> <motorway> role being the destination motorway.

That seems reasonable.  More formally, "onramp/offramp" is based on the
ramp's relation to the highest-classified road it touches; in case of
ties, use "onramp".

> Sometimes, my connector and onramp names look like "<motorway> <direction> 
> / <towards> onramp" e.g. "CA-210 East / Redlands onramp". <towards> is the 
> signed (actually official in CA) destination of the motorway, or a major 
> city along the way.

As I indicated above, I've just been using semicolons for that, since
those seem to be the most common information chung separators in OSM.

> When a link is shared by traffic both exiting and entering the motorway,
> I use a semi-colon-separated list of values. The same applies to the
> situation where one exit ramp for both destination directions leaves the
> originating motorway and then splits into separate links.

In my experience, when one exit ramp later splits for the two directions,
there are usually signes both at the point where the ramp leaves the
highway and where the ramp splits.  What about tagging similarly to the
signage?  The common portion would be tagged, to take an example near me
using your system, "name=I-695 onramp", while the split would be
"name=I-695 North / Towson onramp" and "name=I-695 South / Glen Burnie
onramp".

> Admittedly, much of what is tagged to the ramps can be derived from the 
> related nodes at each end with some work. There just didn't seem to be 
> anyone doing that work, so I wanted to be able to have them make sense when 
> rendered/spoken now, particularly when used by routing.

Yeah, some of the impetus for my questions came out of experimentation
with NavIt, where it seems a little odd not to have any information about
the ramps it tells you to take.  (Although it's not pulling any
information out of the motorway_junction nodes.)

> [2] I'm wishing now that I had used "northbound" instead of "North" after 
> the recent issues with street name expansion, which may create ambiguities.

Well, the exit ramp signage I've seen all uses "North", "South", "East",
and "West".  I don't think it's unreasonable to agree with the signs.

Since this is turning more into a discussion rather than a simple question
and answer, should we move it to talk-us?

-- 
...computer contrarian of the first order... / http://aperiodic.net/phil/
PGP: 026A27F2  print: D200 5BDB FC4B B24A 9248  9F7A 4322 2D22 026A 27F2
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