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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Osm Quality Assessment 2008 Osm Quality Assessment 2008 Presentation Transcript

  • 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]
  • Outline
    • User Generated Geographical Information
    • Open Street Map – background
    • Evaluation and comparison
    • The future of User Generated Content Geographical Information ?
  • 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
    View slide
  • Flickr View slide
  • Geograph.org.uk
    • 7,700 users
    • 1.05m images
    • 71.5% coverage
  • Google Map Maker
  • 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)
  • 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
  • Creating Maps for OSM (Image source: OpenStreetMap)
  • OSM technological stack (cc) OpenStreetMap Haklay, M. And Weber, P., 2008, OpenStreetMap – User Generated Street Map, IEEE Pervasive Computing.
  • 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.
  • (Image source: OpenStreetMap)
  • Mapping parties (cc) Urbanwide - flickr (cc) Nick black (c) Andrea Antonello
  • 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
  • The quality issue
    • How good it the data?
      • Positional accuracy
      • Completeness
      • Attribute accuracy and completeness
      • Consistency
      • Semantic accuracy
      • Temporal quality (up-to-date-ness)
  • 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
  • Who collects?
  • Who collects? (c) Dair Grant (cc) Chris Fleming (cc) Shaun McDonald
  • Working together
  • 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
  • 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)
  • 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
  • Positional Accuracy
    • Meridian 2 and OSM – Motorway comparison
    A B
  • 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
  • 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%
  • Estimating positional accuracy
  • 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
  • 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
  •  
  • London
  • Birmingham
  • Manchester and Liverpool
  • 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
  • Completeness - visual comparison
  • Completeness – visual comparison
  • Completeness
  • Spatial justice and OSM
  • Spatial justice and OSM
  • 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
  • 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
  • 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