How good is Volunteered Geographical Information? A comparative study of OpenStreetMap and Ordnance Survey datasets

Within the framework of Web Mapping 2.0 applications, the most striking example of a geographical application is the OpenStreetMap project. OpenStreetMap aims to create a free digital map of the world and is implemented through the engagement of participants in a mode similar to software development in Open Source projects. The information is collected by many participants, collated on a central database and distributed in multiple digital formats through the World Wide Web (Web). This type of information was termed ‘Volunteered Geographical Information’ (VGI) by Mike Goodchild (2007). However, to date there has been no systematic analysis of the quality of VGI. This paper aims to fill this gap by analysing OpenStreetMap information. The examination starts with the characteristics of OpenStreetMap contributors, followed by analysis of its quality through a comparison with Ordnance Survey datasets. The analysis focuses on London and England, since OpenStreetMap started in London in August 2004 and therefore the study of these geographies provides the best understanding of the achievements and difficulties of VGI. The analysis shows that OpenStreetMap information can be fairly accurate: on average within about 6 metres of the position recorded by the Ordnance Survey, and with approximately 80% overlap of motorway objects between the two datasets. In the space of four years, OpenStreetMap has captured about 29% of the area of England, of which approximately 4% are digitised lines without a complete set of attributes. The paper concludes with a discussion of the implications of the findings to the study of VGI as well as suggesting future research directions.