Anomaly detection for volunteered geographic information: a case study of Safecast data

Volunteered Geographic Information (VGI), defined as geographic information contributed voluntarily by individuals, has grown exponentially with the aid of ubiquitous GPS-enabled technologies. VGI projects have generated a large amount of geographic data, providing a new data source for scientific research. However, many scientists are concerned about the quality of VGI data for research, given the lack of rigorous and systematic quality control procedures. This study contributes to the improvement of quality control procedures by proposing a Cross-Volunteer Referencing Anomaly Detection (CVRAD) method to filter anomalous data, using the crowdsourced Safecast radiation data as a case study. The anomaly detection method is validated using two data sets: (1) an official radiation survey data set collected by the KURAMA car-borne system, (2) a set of anomalous Safecast measurements filtered by Safecast moderators. The validation results show that the proposed CVRAD method outperformed the 1.5 IQR benchmark method in minimizing the overall measurement error and detecting abnormal imports of Safecast measurements, thus demonstrating the effectiveness of the proposed method in improving the overall accuracy of crowdsourced radiation measurements.