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

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

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

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)

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’

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

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.

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

(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

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)

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

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)

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

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

Meridian 2 and OSM – Motorway comparison

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

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%

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

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

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

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

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

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

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

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