## 4 OSM as a Source for Crowdsourced (Indoor) Geodata  
Combining the idea of user generated content (UGC) in the Web 2.0 with the ubiquitous availability of GPS-enabled devices, such as smartphones or cameras, an enormous potential of crowdsourced geodata arises. Both amateurs and professionals collect not only content, but spatially references content, such as geo-tagged Flickr photos or street information (e.g., in FixMyStreet.com). One of the most prominent and most varied source for crowdsourced geodata is OSM. Initially, OSM aimed at the creation of a free world map, but soon the project turned beyond that, becoming more like a free global database comprising different kinds of geodata. Essentially, everybody can contribute, change and improve the data in OSM and the project benefits from currently more than 500,000 registered users [33]. The users can contribute two different types of data: (1) two-dimensional geometries and (2) additional (semantic) information. For the provision of geometries, users basically provide geo-tagged points (_nodes_ in OSM terminology). Currently there are about 1.42 billion _nodes_ inside the database (by end of March, based on our internal OSM database). Additionally, several nodes can be combined into so called _ways_. These can be utilized for either describing inserting geometries or polygons whereas in the former case the way is not closed and in the latter case the way is closed (_i.e._, the last node equals the first node). The current OSM database contains about 131 million _ways_. Furthermore, OSM provides so called _relations_ (currently about 1.35 million) which can be utilized for mapping complex polygons with holes or for describing relationships between different OSM features (e.g., turn restrictions, routes, _etc._). Besides those geometries, users can furthermore tag them, thus provide additional information about them. OSM provides an open key-value pair methodology which allows the contributors to describe a wide range of information and attribution. The key describes a special kind of information domain or characteristic of the map feature (e.g., _building_, _natural_, _etc._) and the value refines this information (e.g., _university_, _forest_, _etc._). There are some community accepted tags which are listed at Watchlist [34], but basically any kind of key/value can be utilized. A complete list of all currently used tags with some exemplary values is available on Tagwatch [35]. Also, the OSM wiki provides detailed descriptions about the different keys and values [36]. Convinced by the increasing demand for indoor data, OSM tries to provide information about indoor spaces, although there is no standard indoor mapping schema available yet. However, a promising and scientifically motivated mapping proposal, namely _IndoorOSM_, has been developed [14] and presented [13]. The application of collaboratively collected _IndoorOSM_ data has already been demonstrated with a web-based two-dimensional indoor map with indoor routing capabilities [37]; however an application which utilizes 3D data of _IndoorOSM_ has not been developed yet. The _IndoorOSM_ model can be described as follows: a building is considered as a hierarchically structured object which consists of several levels/floors. These floors are furthermore divided into elements such as rooms, corridors, stairways, doors or windows. Within OSM, a building is therefore mapped as a relation (main-relation). All the different floors are also mapped as _relations_ (level-relation), whereby these are considered as relation members (children) of the main-relation. Furthermore, the different building parts (rooms, _etc._) are also mapped as relation members of the corresponding level-relation. The _IndoorOSM_ proposal aims at providing detailed floorplan information, thus all building parts are typically mapped as closed _ways_, representing the polygonal footprint of the corresponding building part.