1. The OpenStreetMap project The OpenStreetMap Project is one of the best known examples of Volunteered Geographic Information on the Internet today. The project, which started in 2004, has been successful in providing free high quality spatial data for many towns, cities, and countries in the world. Under a crowdsourcing model OSM volunteers can: collect data manually using a GPS and upload it to the OpenStreetMap database, trace geographic features from freely available aerial imagery (ie Yahoo!), or perform bulk upload from freely available public GIS datasets. Consequently the majority of data in OSM is collected by “non specialists” and “amateur geographers”. This has given rise to serious concerns in the professional GIS community surrounding the spatial data quality of OSM. For OSM to become more widely used by the GIS community “some measures of quality of the data are required”. This will allow data consumers to make informed choices towards reducing or absorbing possible uncertainty or accuracy issues in the OSM data. This poster outlines ongoing research into developing self contained quality indicators for OpenStreetMap data. In many regions of the world it is not possible to obtain ground-truth data to measure the accuracy of OpenStreetMap data against. The establishment of OpenStreetMap-specific quality indicators would provide a useful tool for researchers or potential users of OpenStreetMap data in proving quality evaluations The effects of crowdsourcing on quality in OpenStreetMap Peter Mooney, Padraig Corcoran, Adam Winstanley The spatial data in OpenStreetMap is made available in OpenStreetMap XML (OSM-XML) format. Each time a user successfully edits any feature in OpenStreetMap a new version of that feature is created. Under this model it is possible to trace the spatio-temporal evolution of geographical features in OpenStreetMap. We developed a procedure to download the entire history of any OpenStreetMap polygon (see algorithm box) and calculate a number of characteristics of the polygon: shape characteristics, use of tagging, user interaction, and timestamps. To assist in visualisation within GIS the OSM-XML for each version of the polygon is converted to SHP, KML, and GPX formats. The algorithm can be executed on a frequent basis to include any updates or edits to a given polygon. Introduction Research presented in this poster was funded by a Strategic Research Cluster Grant (07/SRC/I1168) by Science Foundation Ireland under the National Development Plan. The authors gratefully acknowledge this support. v1 v10 v30 v55 Algorithm EXAMPLE The example above shows a forest polygon from the OpenStreetMap database for England (near Exeter). Four versions of the same polygon are shown: v1 the first version, v10, v30, and the current version v55. After each user has made changes to the polygon a new version is stored and subsequently made available. Beneath v1 and v55 are the polygon overlayed on Google Earth aerial imagery for the same region. There are a number of useful observations. 1. While V55 has greater detail the tail at the N-E of the polygon seems incorect in reference to the aerial imagery 2. In V1 the overall shape of the polygon appears to be more accurate based on the visual ground-truth. 3. There are almost two years between the creation of v1 and v55 Methodology SUMMARY FINDINGS Download full history for 500 polygons (200 lakes, 300 forests) All polygons have at least 30 versions of edits Total Number of Polygons = 3145 Mean overall editing time = 858 days Number of invalid polygon versions = 245 (or 8% of 3145) Number of unique contributors per polygon is shown in the histogram below 35% of polygons had a change in overall area (Hectares) of at least 10% of original version