[OSM-newbies] motorway _link and _junction tagging

[Alan Mintz]

At 2010-04-20 13:34, Phil! Gold wrote:
>I'm looking to see how other people approach tagging name= and ref= for
>motorway_links and motorway_junctions.

Yet another subject I've been wanting to write/ask about. Sorry if I should 
have put this in the wiki instead of the list, but I figured we can hash it 
out here before I move it there. I realize it's long. :) It might also be 
better discussed in tagging and then noted back in newbies once it gets 
agreed on? I've therefore Ccd tagging.

Here's the approach I've been using in the LA area. It's gone through a few 
iterations, and so may not be completely consistent.

Examples:

Motorway/street interchange: 
http://www.openstreetmap.org/?lat=34.13614&lon=-117.53647&zoom=17&layers=B000FTF

and motorway/motorway interchange: 
http://www.openstreetmap.org/?lat=34.13521&lon=-117.49705&zoom=16&layers=B000FTF

The information in the tags, though appearing to be free-form, is actually 
formulaic (when I don't make mistakes :) ). Ideally, I'd like to create 
separate tags for the components, or use some other structured solution, 
but I started doing it as a newbie, and just wanted to get on with 
processing my surveys without going 12 rounds with the mailing list on the 
correct structure. All the info is present, and I'm ready to massage it 
into whatever schema is agreed upon.

Here's what I've been doing.

*************************************************
Onramps:

JOSM preset [0]:

<item name="Onramp" icon="entrance_way.png" type="way">
         <label text="Onramp" />

         <text key="source_ref" text="Source Ref" default="" />
         <combo key="source" text="Source" 
values="usgs_imagery;survey;image,etc..." default="usgs_imagery" />
         <space />

         <text key="name" text="Name" default=" onramp"  />
         <text key="ref" text="From" default="from " />
         <space />

         <combo key="highway" text="Highway Type" 
values="motorway_link,trunk_link,primary_link" />
</item>

Tags:

- name: "<motorway name> <direction> onramp" e.g. "CA-210 West onramp" [1].
- ref: "from <street>[ <direction>]" e.g. "from Rosemead Blvd North". 
<direction> is added only when the ramp is accessible from only one 
direction of travel on the street where the ramp originates [2]. When a 
ramp starts on a side street, this may instead look like "from Francisquito 
Ave via Garvey Ave", where the ramp is known as the Francisquito Ave ramp.


*************************************************
Exit node (where offramp joins motorway):

JOSM preset:

<item name="Exit node" icon="exit_node.png" type="node">
         <label text="Exit node" />
         <key key="highway" value="motorway_junction" />

         <text key="source_ref" text="Source Ref" default="" />
         <combo key="source" text="Source" 
values="usgs_imagery;survey;image,etc..." 
default="usgs_imagery;survey;image;CDOT" />
         <space />

         <text key="name" text="Name" default="" />
         <text key="ref" text="Exit #" default="Exit " />
         <space />

         <optional>
                 <text key="milepost:state" text="State MP" default="" />
                 <text key="milepost:county" text="County PM" default="" />
                 <combo key="is_in:county" text="County" 
use_last_as_default="true" values="San Bernardino,Riverside,Los 
Angeles,Orange" />
                 <text key="is_in:city" text="City" default="" />
                 <text key="is_in:state_code" text="State" default="CA" />
         </optional>
</item>

Tags:

- name: "<street>[ <direction>][ <other name>]" e.g. "Azusa Ave North - San 
Gabriel Canyon". The name as official/signed. <direction> is present if it 
is only possible to go in that direction when reaching the target street.
- ref: "Exit <exit number>" e.g. "Exit 23A". The official/signed exit 
number. Note that various states in the US are at different stages of the 
signage installation - it may be necessary to get them from the state DOT's 
docs (that's the "CDOT" in my source tags).
- optional items come from the California DOT. I was originally typing them 
in as I processed each exit, but stopped doing this in favor of doing an 
import when I get around to it.


*************************************************
Exit ramp:

JOSM preset:

<item name="Offramp" icon="exit_way.png" type="way">
         <label text="Offramp" />

         <text key="source_ref" text="Source Ref" default="" />
         <combo key="source" text="Source" 
values="usgs_imagery;survey;image,etc..." 
default="usgs_imagery;survey;image;CDOT" />
         <space />

         <text key="name" text="Name" default=" offramp" />
         <text key="ref" text="Exit #/from" default="Exit nnn from " />
         <space />

         <combo key="highway" text="Highway Type" 
values="motorway_link,trunk_link,primary_link" />
</item>



Tags:

- 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"


*************************************************
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.

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 [3].

When a link is shared by traffic both exiting and entering the motorway, I 
use a semi-colon-separated list of values. Example:

name="I-710 South - Long Beach onramp;I-405 North - Santa Monica onramp"
ref="Exit 32B from I-405 North;Exit 4 from I-710 North"

for this way: http://www.openstreetmap.org/browse/way/26968059

The same applies to the situation where one exit ramp for both destination 
directions leaves the originating motorway and then splits into separate 
links (see freeway interchange example at top). I see, in that example, I 
put both directions in the name key instead of using the semi-colon 
approach - something I'll have to deal with manually.

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.


*************************************************
Notes:

[0] About presets:
- I also add '<key key="created_by" value="" />' to my presets, based on 
the wiki saying this tag has been deprecated, and can be removed when seen.
- For the onramp/offramp way presets, I also add '<key key="oneway" 
value="yes" />' because there was some conflicting info in the wiki as to 
whether this was implied for *_link ways.
- All tags get 'delete_if_empty="true"' though this seems unnecessary now 
(doesn't JOSM do this by default?)

[1] Unlike the ref tag, I hyphenate route numbers (instead of 
space-separating them) when used in a name tag, since the tag is to be 
interpreted by humans, and is more understandable with the hyphen in it.

[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.

[3] This can be particularly useful for those brain-dead (IMO) places where 
they don't bother to indicate the direction on the sign. I almost always 
know what direction I want to go, not always what cities lie in that 
direction, particularly when travelling, when I need it most. The motorway 
doesn't even always go to the named destination. I think at some point 
north of LA, I-5 says "San Francisco", but it doesn't come within 60 miles 
of the city.</rant> :)

--
Alan Mintz <Alan_Mintz+OSM at Earthlink.net>