Osm Quality Assessment 2008

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

Flickr

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

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

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Osm Quality Assessment 2008

by mukih on Jan 12, 2009

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