Abstract:In the area of Volunteered Geographical Information (VGI), the issue of spatial data quality is a clear challenge. The data that is contributed to VGI projects does not comply with standard spatial data quality assurance procedures, and the contributors operate without central coordination and strict data collection frameworks. However, similar to the area of open source software development, it is suggested that the data holds an intrinsic quality assurance measure through the analysis of the number of contributors who have worked on a given spatial unit. The assumption that as the number of contributors increases so does the quality is known as 'Linus' Law' within the Open Source community. This paper describes three studies that were carried out to evaluate this hypothesis for VGI using the OpenStreetMap dataset, showing that this rule indeed applies in the case of positional accuracy.

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Are Land Owners able to participate in official Cadastral Surveys? Can the official procedures be modified in order for crowdsourcing techniques to be incorporated in them? How many different stakeholders can actively get involved and which is the optimum workflow that could be adopted? This chapter addresses the main question of whether the spatial and attribute data that is collected by volunteers -land owners -can be used in official Land Administration Systems (LAS) and explores the potential introduction of crowdsourcing techniques into the official cadastral surveys as a simplified and transparent procedure with the aid of citizens.As the title reveals, this chapter aims to propose a crowdsourcing cadastral model as an alternative option to the official cadastral procedures. The research investigates a voluntary model and documents it in terms of participants and structure according to various international case studies that were analyzed in depth within the research that was carried out by Haklay et al. (2014). The main lessons that were collected by each separate crowdsourced case study were used as a guideline for the suggested cadastral model. The opportunities and the weaknesses are isolated and explored in terms of a cadastral survey. The main advantage of the adopted case studies is the opportunity for a simulation of 420 European Handbook of Crowdsourced Geographic Information real circumstances in cadastral surveys and not a simplistic logic. Τhe main innovation is focused on the design of the model in an a priori approach with well-defined and already tested successful case studies.The model is clarified in technical and societal aspects while it sheds light on the proposed process. The workflow, the stakeholders and the adopted main lessons of the crowdsourced case studies are the key components that are explored and analyzed in this chapter.