Talk:Key:exit to

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Discussion about deprecating exit_to

The following is an excerpt from the tagging mailing list.

  • Carlosz22
I started using this tag for exits on underground (metro) as a complement with their name. For example, in Madrid the Station Gran Vía has 4 diferents exits, one of them it's tagged: Name= Gran Vía; exit_to=Calle Jacometrezo. I think this can be really useful to know what it's the correct exit in the underground to go where you want. Some exits in the underground can be separated more than 500 meters. Now it's time to the render start use it.


  • Johan C
On http://wiki.openstreetmap.org/wiki/Tag:highway%3Dmotorway_junction you can find the following description on the exit_to tag. 'exit_to=* should be used to detail the destinations where the junction exits to—for example, if signage states a road leads to Anytown on the A1000… exit_to=Anytown A1000; if multiple destinations are shown on signage, tag them with semicolons: for example, exit_to=Anytown A1000; Elsewhere A1001; Anyvillage; note that Anyvillage doesn't have a ref number'
Unfortunately, exit_to is not documented. The destination in my opinion has same purpose as exit_to, but is a better choice because you can use it on both outgoing parts of the Y-branch and because you can use in in conjunction with destination:lanes.
  • Philip Barnes
IMHO the most important thing to tag a motorway exit with is its number.
  • malenki
> Do you see any sense in using exit_to or destination?
no
What is the use of tagging some examples where one road connects to when there is a system-inherent focus on finding such connections automagically (this one is called "Routing")?
  • Colin Smale
Johan, I agree with your statement that "destination" is much more universal than "exit_to". I would prefer to see "destination" brought into wider use and "exit_to" deprecated. I only use "destination", which I use very frequently to help make routing instructions (not: routing calculations - these have nothing to do with destination tags) more closely reflect landmarks on the ground (i.e. large signs at junctions).
  • Philip Barnes
I found this one by accident when I was looking at motorway junctions after reading this thread.
http://www.openstreetmap.org/?lat=52.65853&lon=-2.29423&zoom=15
Eastbound Wolverhampton (W) A41
Westbound Whitchurch A41;Weston
They are just copied from the signposts. I see no value in this tag, after all as you say its called routing.
  • Colin Smale
Phil, there's a difference between routing calculation (which neither knows nor cares about road names, numbers, signposts etc) and how the result of the calculation is presented to the user. Then you need to relate the nodes/edges in the routing graph back to the real world. The value in this tag (as well as name, destination etc) is that the navigation software can give instructions based on recognisable landmarks instead of referring to way IDs. This distinguishes between pure "routing" and "useful navigation".
  • Tobias Knerr
> 4. is it clear for you when to use exit_to and when to use destination?
Yes: Don't use exit_to anymore. ;)
> 5. do you have any problems (and if so: which ones) when the exit_to description is removed from the wiki?
It's still in the database, so someone encountering it should be able to learn what it means. However, I suggest to prominently point out the existence of destination as a superior alternative where that isn't already the case.
  • Philip Barnes
> The value in this tag (as well as name, destination etc) is that the navigation software can give instructions based on recognisable landmarks instead of referring to way IDs. This distinguishes between pure "routing" and "useful navigation".
Thats the point I am making, the most useful instruction a satnav can give is "leave the motorway a junction 4", or words to that effect. There is nothing more recognisable than the junction number.
  • Mike N
In the US, some junctions don't have a ref, so a useful instruction from the sat nav "Take the exit to US4 / South Bay".
  • Colin Smale
> Thats the point I am making, the most useful instruction a satnav can give is "leave the motorway a junction 4", or words to that effect. There is nothing more recognisable than the junction number.
Well, for a start junctions are only numbered on motorways and some trunk roads. I think most people would consider "keep left on the A1001 towards Anytown" clear enough (assuming that's what's on the sign), with or without a junction number. There has also been a discussion going on (admittedly outside of the UK) about the use of destination:ref to store the ref of the destination, so in this case we would have destination=Anytown and destination:ref=A1001, plus junction:ref=5 or whatever. By structuring the information in this way we give navigation software the choice of how to present the data.
  • Paul Johnson
What about relations? I seem to recall relations exist for this.
  • Martin Vonwald
IMO the key destination is the better choice and much more powerful than exit_to. But if we remove any mentioning relating to exit_to from the wiki, next week(TM) someone will re-discover this key and reuse it, maybe even create the "missing" documentation. And the week after we have to start this discussion again. (And again next month).
The key exit_to is used over 22.000 times. We definitively should mention it in the wiki, even if we just state that it is deprecated. When looking on the map of this key I see that it is used mainly in france, belgium, the netherlands and the US. I think it would be a good idea to post this also in the related mainling lists.
  • Simone Saviolo
In this motorway intersection [1], where there's no evident "exit lane", the difference between "follow right", "follow right to the A8/A26 motorway", and "follow towards Gallarate, Malpensa, Milano" is crucial. Of course we could have navigators ( != routers) that only tell us to go right and left, but having they call roads by their name it's a great help. In that case, there would be a large overhead sign with an arrow pointing towards "Milano (A8)" and another one towards "Gravellona Toce (A26)", and those would be the easiest instructions to follow, since you'd be already looking at the sign anyway (even better than right/left).
In non-motorway situations this would be great instructions too. Suppose you're driving along a long straight road, and there are two crossroads close to each other (say, about 50 metres away). I would be hesitant to pick one of them based only on an instruciton like "in 100 metres, turn left" - an instruciton that is given as I'm driving, for example, at 70 km/h, which is about 20 m/s. However, if I was told "turn left to ThatVillage", I would quickly match the instruction to a sign on the ground, and I would safely and surely taking the correct turn.
[1] http://www.openstreetmap.org/?lat=45.69585&lon=8.54584&zoom=16&layers=M
  • Martin Vonwald
I think that someone mentioned somewhere that exit_to is used in some template in some editor (yes, I don't remember it perfectly) - maybe potlatch? Can someone verify this? If we want to deprecate exit_to we should remove it from that template.
  • William Rieck
maybe the reference to a template was to this wiki page http://wiki.openstreetmap.org/wiki/Tag:highway%3Dmotorway_junction where it seems to emphasize the 'exit_to' key over 'destination'
  • Johan C
JOSM supports exit_to. JOSM doesn't support destination. Following the text by Martin I updated http://wiki.openstreetmap.org/wiki/Tag:highway%3Dmotorway_junction#Destinations. I indeed think it's a good idear to be clear in the communication of any (to be) deprecated tag. Most exit_to's seem to be used in the US. I checked upon a motorway_junction in the US (New York) where I noticed that the name=* of the motorway_junction had been replaced by exit_to=* with the same value. The US does not seem to use the name=* on the motorway_junction. Two questions on that:
1. does the tag exit_to=* on a motorway_junction in your opinion have the same meaning as the tag name=* on that motorway_junction?
2. if your answer to the first question is no, than what is the difference?
  • Mike N
Some motorways in the US have formal names assigned to exits, some are informal - the exit is always referred to by a name on the traffic report for example. This is distinct from the destinations on the sign. The Pennsylvania Turnpike has formal exit names - for example http://www.paturnpike.com/ConstructionProjects/mp199to202/images/exit_sign.jpg
  • NE2
exit_to is what's on the sign. name is a name given to the interchange, which doesn't usually exist in the U.S. A few examples where it does exist (mainly on toll roads):
<http://www.alpsroads.net/roads/pa/i-276/e343.jpg> name=Willow Grove exit_to=PA 611; Doylestown; Jenkintown
<http://www.aaroads.com/northeast/massachusetts050/i-090_wb_exit_008_04.jpg>
<http://www.alpsroads.net/roads/ma/i-90/ticket.jpg> name=Palmer exit_to=SR 32 to US 20; Palmer; Amherst
I know there was a discussion somewhere about replacing name with exit_to, but I don't remember where. Thus the wheel is being reinvented for no reason.
  • Richard Welty
there are quite a few named interchanges in South Carolina, as i recall. frequently named after State Troopers who were killed in the line of duty. the name is not at all the same as the value of exit_to
  • Paul Williams
I don't see any reason to deprecate exit_to, it seems to be the simplest method of mapping a destination sign on a motorway junction or similar exit. I use exit_to fairly frequently and it has been a documented tag for a while (although on the motorway junction page rather than it's own page) and is also used in JOSM presets.
I feel it is a less ambiguous tag than destination (as a tag on a way) as it shows the specific point where a destination is signed, unlike destination tagged on a way. If you use destination as a tag on a way then I think you'd need to be sure that at every point along that way the destination(s) given is the same throughout and if not or you didn't know you'd need to split the way. The Taginfo stats also seem to show that exit_to is the most popular of the three different ways of mapping destinations: a destination relation, exit_to on a junction node, or destination as a tag on a way.
A destination relation is also a clear way of mapping a destination as the intersection and both the 'from' and 'to' ways are part of the relation, and is particularly useful in mapping situations where exit_to wouldn't work (like at a crossroads) so I do also use this method. It is however more complex (and so is unlikely to be a method that a new mapper would be able to use) particularly where there are multiple destinations given on a sign which requires a relation for each destination.
  • Johan C
The fundamental question is: where do you store the information needed for any router, in a node, in a way or in both? In my opinion destination on a way can work very well, please take a look at this example: http://wiki.openstreetmap.org/wiki/User:It's_so_funny
  • Paul Williams
I don't know about storing information for a router, I'm just speaking from the perspective of myself as a mapper and saying that to me exit_to on a junction node seems a simple and established way of recording exit destination signs, so I don't see why I and other mappers using exit_to should change from this. On a simple short one way motorway slip road with just one road leading on to it, as in your example, I can see that destination tagged on the way probably wouldn't be a problem. However on longer and more complex ways you'd need to make sure that the roads were split before every junction - to identify the point where the destination is signed, as the destination(s) could change at different points along that road.
  • Tobias Knerr
> I don't see any reason to deprecate exit_to, it seems to be the simplest method of mapping a destination sign on a motorway junction or similar exit.
Isn't adding a destination tag to the outgoing highway fork just as simple? When you have two tags where one (destination) can express all the information described by the other (exit_to), but not the other way around, then deprecation of the less powerful variant is the logical course of action. The only alternative would be permanently having two tags for (largely) the same situation, which makes documenting, evaluation for applications, and providing assistance in editors harder than it needs to be.
> The Taginfo stats also seem to show that exit_to is the most popular of the three different ways of mapping destinations: a destination relation, exit_to on a junction node, or destination as a tag on a way.
I think that nobody contests this, but it's to be expected given the existence of a JOSM preset and the current state of the documentation. The difference in usage isn't that large even today, though.
  • Colin Smale
Using only exit_to there is no way to handle junction topologies other than a straightforward highway exit, where there is one "big" through road and one "small" road leaving. What about wrong-side exits? Or where the highway splits into two (or more) roads of equal importance?
Destination tagging is used a lot in the Netherlands, placed on the first segment of each way *after* the node where they split. My Garmin warns me ahead of time which side to keep to, so there doesn't seem to be a need to start the tagging at the first sign (which may be 1km or more before the actual junction). I have not yet found a case where adding destination=* around a junction felt like the wrong thing to do. IMHO destination=* on the ways is the right balance between the rudimentary exit_to on the node and using a relation which will have problems with support/adoption by both mappers and toolmakers.
  • Johan C
Overlooking the discussion so far, I think exit_to cannot be deprecated. However, there's strong feelings to support both destination and exit_to. In my opinion, the following things can be done:
1. keep things the way they are now (where exit_to is the preffered choice, because the text on the motorway_junction page states that it should be used). The disadvantages of exit_to are not solved:
a. no description of exit_to
b. no solution of the exit_to_left yet to support both branches
c. not clear why other items of a exit ramp are not used in the motorway_junction tag (like lanes, maxspeed)
d. no support for advanced lanes tagging to summarize: no support for a lane assistant
2. deprecate destination
disadvantage the same as above, so no support for a lane assistant
3. deprecate exit_to
several U.S. OSM'ers do want to keep on using exit_to
Possible solution in this discussion. The non-U.S. OSM'ers in this discussion seem to favour destination. The U.S. OSM'ers seem to favour exit_to. Lets split it in the text of motorway_junction tag. I do have a text suggestion for that. Please send your thoughts on this. You can see I also try to adress the realtion discussion, which I think can be handy, but I don't see the value for motorway exit tagging. Destination can do the trick there, and a relation is more complex = less KISS
Destination
The tags destination <http://wiki.openstreetmap.org/wiki/Key:destination>=*, destination:ref <http://wiki.openstreetmap.org/wiki/Key:destination:ref>=* (according to information on road signs) and *lanes*=* should be used on the ways directly after the exit. The tag destination:lanes<http://wiki.openstreetmap.org/wiki/Key:destination>=* can be used on complex motorway_junctions. These tags are needed to support a lane assistant in navigation devices.
In the United States exit_to<http://wiki.openstreetmap.org/wiki/Key:exit_to>=* on the motorway_junction node should be used to detail the destinations where the junction exits to. The tag Relation:destination_sign<http://wiki.openstreetmap.org/wiki/Relation:destination_sign> can be used in non-motorway situations.
This part of the exit_to will in my text suggestion be moved to the exit_to Wiki page:
—for example, if signage states a road leads to Anytown on the A1000…exit_to <http://wiki.openstreetmap.org/wiki/Key:exit_to>=Anytown A1000<http://wiki.openstreetmap.org/w/index.php title=Tag:exit_to%3DAnytown_A1000&action=edit&redlink=1>;if multiple destinations are shown on signage, tag them with semicolons: for example, exit_to <http://wiki.openstreetmap.org/wiki/Key:exit_to>=AnytownA1000; Elsewhere A1001;Anyvillage<http://wiki.openstreetmap.org/w/index.php?title=Tag:exit_to%3DAnytown_A1000;_Elsewhere_A1001;_Anyvillage&action=edit&redlink=1>; note that Anyvillage doesn't have a ref number.
  • James Mast
> b. no solution of the exit_to_left yet to support both branches There is a solution in the form of this proposal that I made awhile ago that nobody really commented about here on the Tagging list or on the Wiki page for it.http://wiki.openstreetmap.org/wiki/Proposed_features/motorway_junction_Extension --James
  • Martin Vonwald
From the taginfo map I wouldn't expect that we could find a global solution. I therefore would document both solutions (destination is already documented, preferable someone from the US has to properly document exit_to) and state in the articles about motorway_junction and exit_to that exit_to is mainly used in the US and some other countries that want to stick with exit_to. This of course is not really a solution as data consumers have to implement two tagging approaches - and I doubt that every one will do this. But well - any better suggestions?