## 1 Introduction  
The OpenStreetMap (OSM) project has a history of nearly seven years now (2011). Similar to Wikipedia, the information gathered can be described as User-Generated Content (UGC) [1,2]. However, unlike Wikipedia, it is not encyclopedia information that is being gathered; instead, users are contributing their geodata to OSM. This data of geographical relevance is compiled by volunteers, saved in a database, and made 'freely' available to everyone via the World Wide Web (WWW) [3,4]. OSM is a well-known project in the field of Volunteered Geographic Information (VGI) [5, 6, 7], which others also describe as crowd sourced (geodata) [8, 9, 10, 11]. Furthermore, especially in connection with the term of Web 2.0 [12], it is also referred to as Neogeography [13, 14, 15, 16, 17]. Others again describe it as Collaborative Mapping [18] or the Wikification of GIS [19]. The successful development of user generated content in recent years had an increasing impact on a variety of research fields and particularly OSM has been the focus of many new developments such as routing applications, 3D city models and Location-Based Services (LBS) [20, 21, 22, 23]. Within the past few years, the OSM membership numbers have rapidly developed from a few hundred in mid-2004 to more than half a million registered members in November 2011. But what drives such a large number of people to participate in a voluntary project, and where lies their motivation? A few suggestions have been made to describe the motivation of the volunteers, such as a certain need for self-representation by the members or the project's fun factor, and a degree of interest in technical terminology, equipment, and the WWW [7]. Either way, according to our research, approximately 150 new active members have joined the project each day since the beginning of 2011. Despite these numbers, OSM tends to experience a problem that is similar to other online portals that are based on UGC: participation inequality. This term describes the phenomenon of a 90-9-1 rule that most of the projects inherit [24]. Ninety percent of all members merely consume and are described as lurkers, 9% contribute to the project at irregular intervals, and just 1% of the members is actively involved and counts for the largest number of contributions to the project. A similar scenario exists within the OSM project. At the beginning of 2008 there were 30,000 total members in OSM, and about 10% of them actively contributed to the project [11]. In 2009, there were approximately 200,000 registered members, yet still, only roughly 10% of these were active members [25] and contributed to the project. In the same year 98% of all project data was provided by approximately 5% about 10,000 members. In 2010, only 5% of the 330,000 members were active contributors, and 98% of the data was provided by about 3.5%, which represents 12,000 of the total registered members. While some countries such as the USA and France imported large datasets from other providers of freely available data (e.g., from governmental agencies such as the US Census Bureau), within the scope of the project, in Germany, OSM relies on its large number of participants. In 2009 nearly 50% of the entire changes in the OSM database were made within Germany [26]. However, in 2010 this value lowered to approximately 30%. Despite this decrease, the aforementioned numbers give a first impression of how the OSM project has become a potential competitor to public and commercial geodata providers, not just in Germany but also worldwide. We see a revolutionary paradigm shift on how map data is being collected. MapQuest and Bing Maps are some of the first international companies that are reacting to this trend and have started offering maps based on OSM data (e.g., open.mapquest.com) or additional LBS's such as route planning, and address and area search functions on their websites.