Volunteered Geographic Information (VGI) is a widely used data source in various fields and services, such as environmental monitoring, disaster and crisis management, SDI, and mapping. Quality is a critical factor for the usability of VGI. This study focuses on evaluating logical consistency based on the topological relationships between geographic features while considering semantics. It addresses internal (i.e., between thematic layers) and external (i.e., between specific features from different thematic layers) logical consistency. Attribute completeness is computed to support the use of semantics. A tool for assessing the consistency and attribute completeness is designed and implemented in the ArcGIS environment. An open-source web mapping application informs users about VGI consistency with multiscale visualization and indices. Data from OpenStreetMap (OSM), one of the most popular collaborative projects, are evaluated for six European cities: Athens, Berlin, Paris, Utrecht, Vienna, and Zurich. The case study uses OSM-derived data, downloaded from Geofabrik and organized into thematic layers. OSM’s consistency is evaluated and visualized at the regional, city, and feature levels. The results are discussed and conclusions on attribute completeness and consistency are derived.

The visualization of semantic information provides new ways for knowledge acquisition and access, since it enables users to explore and understand the meaning of information, as well as to identify associations among data and connections to existing knowledge. Maps on the other hand are extensively used as symbolic representations of spatial reality. Lately, researchers have delved deeper into formalizing the connection between the map and the semantics it conveys using knowledge-based formalisms such as knowledge graphs, ontologies, and linked data. Semantic visualization techniques may also enrich maps with the knowledge immanent therein and support knowledge visualization and exploration.The present paper describes the development of a web-based prototypical application that contains a spatial and a semantic component that interact. In addition to the representation of geospatial entities as cartographic features, the graph-based representation of semantic information is also implemented, to enable users to explore and understand the meaning and semantic relations between concepts and entities that appear on the map.