The location of an event or feature on the Earth's surface can be used to discover information about the location's surrroundings, and to gain insights into the conditions and processes that may affect or even cause the presence of the event or feature. Such reasoning lies at the heart of critical spatial thinking, and is increasingly implemented in tools such as geographic information systems and online Web mashups. But the quality of contextual information relies on accurate positions and descriptions. Over the past two decades substantial progress has been made on the theory and methods of geospatial uncertainty, but hard problems remain in several areas, including uncertainty visualization and propagation. Web 2.0 mechanisms are fostering the rapid growth of user-generated geospatial content, but raising issues of associated quality.