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Osm Quality Assessment 2008

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OSM Quality Assessment - presented in S4 event, London, 8th Jan 2008

OSM Quality Assessment - presented in S4 event, London, 8th Jan 2008

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    • 1. Understanding the quality of user generated mapping – comparing OpenStreetMap to Ordnance Survey geodata Dr Muki Haklay Department of Civil, Environmental and Geomatic Engineering, UCL [email_address]
    • 2. Outline
      • User Generated Geographical Information
      • Open Street Map – background
      • Evaluation and comparison
      • The future of User Generated Content Geographical Information ?
    • 3. User Generated Geographical information
      • Easy to use mapping websites, and wide availability of base mapping
      • Capture devices – from GPS receivers to mobile phones with integrated camera and A-GPS
      • User Generated Content – Flickr, YouTube
    • 4. Flickr
    • 5. Geograph.org.uk
      • 7,700 users
      • 1.05m images
      • 71.5% coverage
    • 6. Google Map Maker
    • 7. OpenStreetMap
      • User generated (Crowdsourced)
      • Wiki style
      • Open access to data and software
      • ‘ OpenStreetMap is a project aimed squarely at creating and providing free geographic data such as street maps to anyone who wants them’
      (Image source: OpenStreetMap)
    • 8. OpenStreetMap
      • Started at UCL by Steve Coast, in the summer of 2004, with the aim to create a crowdsourced street map of the world
      • Many people joined in to help with the technical infrastructure and collect data. About 40-50 people form the core of the organisation
    • 9. Creating Maps for OSM (Image source: OpenStreetMap)
    • 10. OSM technological stack (cc) OpenStreetMap Haklay, M. And Weber, P., 2008, OpenStreetMap – User Generated Street Map, IEEE Pervasive Computing.
    • 11. Simplified glue – OSM API vs. OGC WMS
      • OpenStreetMap API: http:// api . openstreetmap.org / api /0.5/map?bbox=-71.00,42.00,-72.00,43.00
      • OGC WFS API:
      • http://example.com/wfs?service=WFSSIMPLE&version=0.5&REQUEST=GetFeature&BBOX=-71.00,42.00,-72.00,43.00&TIME=2006-09-12/2006-09-22&OUTPUTFORMAT=text/xml
      Haklay, M. And Weber, P., 2008, OpenStreetMap – User Generated Street Map, IEEE Pervasive Computing.
    • 12. (Image source: OpenStreetMap)
    • 13. Mapping parties (cc) Urbanwide - flickr (cc) Nick black (c) Andrea Antonello
    • 14. Achievements
      • Tens of thousand of participants
      • Companies formed to commercialise outputs (CloudMade, Geofabrik)
      • Coverage of many places around the world where there is no commercial coverage by Teleatlas or Navteq
    • 15. The quality issue
      • How good it the data?
        • Positional accuracy
        • Completeness
        • Attribute accuracy and completeness
        • Consistency
        • Semantic accuracy
        • Temporal quality (up-to-date-ness)
    • 16. The problem
      • We know little about the people that collect it, their skills, knowledge or patterns of data collection
      • Loose coordination and no top-down quality assurance processes
    • 17. Who collects?
    • 18. Who collects? (c) Dair Grant (cc) Chris Fleming (cc) Shaun McDonald
    • 19. Working together
    • 20. Number of Users Area covered (Sq Km) 1 40021 2 20720 3 9136 4 4184 5 1986 6 936 7 448 8 269 9 139 10 and above 246
    • 21. Users
      • Participation inequality – small group of users collect most of the information, lots of users collect very little
      • Little ‘on the ground’ collaboration. Important as this is the main source of quality assurance in open source project - ‘Given enough eyeballs, all bugs are shallow’ (Raymond, 2001)
    • 22. Accuracy and Completeness
      • Comparing OSM to OS Meridian 2 roads layer
      • Maridian 2 -Motorways, major and minor roads are... Complex junctions are collapsed to single nodes and multi-carriageways to single links... some minor roads and cul-de-sacs less than 200m are not represented... Private roads and tracks are not included...
      • Nodes are derived from 1:1,250-1:2,500 mapping, with 20m filter around centre line generalisation
    • 23. Positional Accuracy
      • Meridian 2 and OSM – Motorway comparison
      A B
    • 24. Goodchild and Hunter (1997), Hunter (1999) method
      • Assuming that one dataset is of higher quality
      • Create buffer around the dataset with known width
      • Calculate the percentage of the evaluated dataset that falls within the buffer
    • 25. Motorway comparison
      • Buffer of 20m
      • Average of 80% - ranging from 59.81% to 88.80%
      Motorway Percentage Overlap M1 87.36% M2 59.81% M3 71.40% M4 84.09% M4 Spur 88.77% M10 64.05% M11 84.38% M20 87.18% M23 88.78% M25 88.80% M26 83.37% M40 72.78% A1(M) 85.70% A308(M) 78.27% A329(M) 72.11% A404 76.65%
    • 26. Estimating positional accuracy
    • 27. Positional accuracy
      • On each tile, 100 points sample with evaluation of distance between OSM and Meridian 2
      • Can see significant differences: from about 3m to over 8m
      Area Average difference (m) Barnet 6.77 Highgate 8.33 New Cross 6.04 South Norwood 3.17 Sutton 4.83 Total 5.83
    • 28. Completeness – bulk method
      • Assumption: as Meridian 2 is generalised, for each completed sq km:
        • Total length(OSM roads)>Total length(Meridian 2 roads)
      • Dividing England to 1km grid squares, and running a comparison for each cell
    • 29.  
    • 30. London
    • 31. Birmingham
    • 32. Manchester and Liverpool
    • 33. Length comparison
      • For 29.3% of the area of England, OSM is getting nearer completion and as good as Meridian 2
      • When adding to this attributes, the percentage drops to 24.5%
      • Centres of major cities are well mapped
    • 34. Completeness - visual comparison
    • 35. Completeness – visual comparison
    • 36. Completeness
    • 37. Spatial justice and OSM
    • 38. Spatial justice and OSM
    • 39. So should I use OSM?
      • OSM is fit for many purposes to which Meridian is suitable
      • Positional accuracy is satisfactory
      • Completeness in major urban area is satisfactory – and if the work is at a specific location, it is easy to improve and complete the dataset
    • 40. Conclusions
      • Impressive coverage by 150 participants with some help of 1000+ others
      • Possible to see completion within 3 years
      • Open questions: motivation, longevity of engagement, quality and multiple users, comparison with detailed datasets (MasterMap), giving information to participants about completion
    • 41. Further reading
      • Haklay, M., 2008, How good is OpenStreetMap information? A comparative study of OpenStreetMap and Ordnance Survey datasets for London and the rest of England , submitted to Environment and Planning B.
      • Haklay, M. And Weber, P., 2008, OpenStreetMap – User Generated Street Map , IEEE Pervasive Computing.
      • Haklay, M., Singleton, A., and Parker, C., 2008, Web mapping 2.0: the Neogeography of the Geoweb , Geography Compass
      • Haklay, M., 2008, Open Knowledge – learning from environmental information , presented at the Open Knowledge Conference (OKCon) 2008, London, 15 March.
      • Haklay, M., 2007, OSM and the public - what barriers need to be crossed? presented at State of the Map conference, Manchester, UK, 14-15 July.
      • To get a copy, write to [email_address] , or get them on povesham.wordpress.com