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I posted the following question on the main StackOverflow website, but was informed that I might get a better response here. Hence I'm copying it below. Note however, that I have an active bounty on the original posting.


I have been using a commercial solution for route distances and travel times for North America and Western/Mid Europe. I am considering expanding the project to cover other countries - and perhaps the entire world. A very limited budget and patchy regional coverage from individual commercial providers, probably make locally-hosted OpenStreetMap the only viable option. Before someone suggests an online solution, my application requires a lot of intensive route calculation - something which would cost a lot or be very impolite (and probably banned) if performed using a web service. The results of the calculations are put back in the public domain, so rediting OpenStreetMaps is not a problem.

My problem is how do I assess the routing data coverage for individual countries in the OpenStreetMap database? Such an assessment could determine if the project is viable, and a suitable order for processing (ie. do the countries with the best coverage first).

High-end commercial data providers can typically supply statistical descriptions, as well as regional descriptions of surveyed coverage. OpenStreetMap is much more patchy - an area typically includes some roads, but not all roads. Individual location errors of a few metres of even 10-20m will not be a problem for my application (I'm looking at city-city distances), but route graph connectivity is. Ie. the road vectors must logically meet correctly at a junction.

Has anyone attempted to create statistics describing data coverage of the OpenStreetMap database?

If not, how would you go about it?

The best I can think of is to take a random sampling of places (eg. cities), and then attempt to calculate routes. There would have to be an assumption that the major roads will tend to be added before the minor roads. Therefore a route between two distant cities would use the logical major road, and not a minor road (which is typically longer/slower) because the major road is missing.

Another problem would be that it is physically not possible to drive between many towns. Often this is due to the presence of islands (where ferries could be used) but often there is no surface route (eg. settlements in Nunavut). So how would such statistics be used when comparing between (say) Tonga and Afghanistan. Afganistan probably has very low data coverage. Tonga is probably better but the settlements are spread out across an archipelago.

Some details about my application: All start and end points are towns and cities with locations taken from the Geonames database. Typically I am looking at the 1000 largest cities in a country that also have a population of at least 1000. Routes are currently calculated in duplicate as both fastest routes and shortest routes. Reasonable road speeds vary according to broad road categories. Estimated travel times are computed alongside road distances. These details are preferences for consistency- they are not set in stone.

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4 Answers

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There's no statistics on routing quality in different countries available, as far as I'm aware. The best thing you can do is try to measure things indirectly.

I organised a project to do this in the USA on OpenStreetMap during 2009. For full details see the 250 cities project on the OpenStreetMap wiki

First we measured how many of the 250 largest cities in the country were routable, in a large matrix of every possible start/finish point. Secondly, we found places where the outward/backward routes were significantly different lenghts. Then we looked at routes where the distance was greater than 1.4x of the great-circle route, as an indication of likely routing problems.

You could use a similar approach to estimate routing quality in your countries of interest. Your assumption that major cities and major roads are mapped first generally holds true for OpenStreetMap, in my experience.

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Thanks GravityStorm. Comparing out and back is a good idea. My experience with products like MapPoint is that there can be up to 2-3 miles difference (usually < 1mile) for US routing. For the 1.4x factor I suspect this varies a lot be area. Somewhere like the Scottish Highlands&Islands (or a sparsely populated mountainous area) could easily be bigger than this. –  winwaed Nov 22 '10 at 15:01
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http://wiki.openstreetmap.org/wiki/YOURS

demo:

http://www.yournavigation.org/

*dependent on the coverage and data structure of OSM data for the area of interest.

Example from the API http://www.yournavigation.org/api/1.0/gosmore.php?format=kml&flat=52.215676&flon=5.963946&tlat=52.2573&tlon=6.1799&v=motorcar&fast=1&layer=mapnik returns an xml for KML (Google Earth)

Further Info: http://wiki.openstreetmap.org/wiki/Gosmore

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Thanks - those links will be useful when I come to choose a suitable routing engine. However, I can't see any answers to my question of coverage? –  winwaed Nov 10 '10 at 20:34
    
But OSM is not based on region. It is continually being worked on so you need to know the limitations of the data source. Having the Roads for a state/county/province doesn't make routable it requires the right setup - try wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin/Download for countries for garmin gps for a guide. –  Mapperz Nov 10 '10 at 20:42
    
Exactly. As it is being actively worked on and many roads are missing, how would I go about creating an assessment of the road network in a particular area? Ie. to determine if it is "good enough" for my application? –  winwaed Nov 10 '10 at 20:49
    
without referencing to any other [copyright] data it is hard - it's based on local knowledge and checked/confirmed by other contributors. All GIS data has errors its just minimising them. The bigger the coverage the more errors are likely. Always a challenge... –  Mapperz Nov 11 '10 at 4:35
    
Indeed, and it seems that this is a particular weakness of the OSM method. A commercial surveyor and look at errors/changes when re-surveying and at least come up with an estimate of the errors present in the rest of the database. –  winwaed Nov 16 '10 at 15:03
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The guys over at Open Route Service claim to be able to do routing across Europe from OSM data.

http://openrouteservice.org/

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I am going to be doing the routing "offline" - I require a lot of processing and it would very very impolite (or pricey) to hit a web service in this manner. –  winwaed Nov 11 '10 at 13:05
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Would it be feasible to do something like:

  1. Pick two random points (town names perhaps)
  2. Use an OSM router (even http://map.project-osrm.org/ maybe) to calculate distance
  3. Use a commercial router or three (eg, Google Maps, Bing Maps, Mapquest) to calculate distance
  4. Compare OSM distance vs commercial distance
  5. Repeat x1000 (or x10,000 or whatever seems reasonable and doesn't violate anyone's terms and conditions).

The results could be interesting. If the average OSM route is 105% as long as the average Google Maps, is that good enough? What if 5% of the time it's more than 25% longer? etc.

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