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 protected]

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 400212 207203 91364 41845 19866 9367 4488 2699 13910 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

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%

• Buffer of 20m

• Average of 80% - ranging from 59.81% to 88.80%

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 protected] , or get them on povesham.wordpress.com