2021:  A proposal for a QGIS Plugin for Spatio-temporal analysis of OSM data quality: the case study
Channel: State of the Map
Date: 2021-10-12

https://media.ccc.de/v/sotm2021-academic-10424-a-proposal-for-a-qgis-plugin-for-spatio-temporal-analysis-of-osm-data-quality-the-case-study-for-the-city-of-salvador-brazil



It Consists in a proposal for a QGIS Plugin for Spatio-temporal analysis of OSM data quality in an area of Brazil.

The development of methodologies to evaluate geospatial data quality is one of the most important aspects to be considered while obtaining these data. For the developing countries, such as Brazil, the lack of investment for the maintenance of the topographic mapping, especially on a big scale, is a recurrent challenge to the National Mapping Agencies (ANM) [1]. For example, studies reveal areas in Brazil that have never been mapped and that the topographic mapping in the 1:25.00 scale is nearly 5% of its extension [2].
The technological advances enabled a series of methodologies for obtaining geospatial data [3]. One example is presented as Volunteered Geographic Information (VGI) [4]. In this case, the update of information may occur faster and with a reduced cost in detriment to the traditional structures of topographic mapping [5]. A successful case of VGI is the OpenStreetMap (OSM) platform, which presents the growth in the number of contributors and contributions or mapped features. To comprehend the behaviour of the OSM features and their integration potential to the topographic mapping, different surveys worldwide have put efforts to evaluate its quality, whether by its extrinsic [6, 7] or intrinsic [8] aspects. In this regard, some studies have evaluated the quality of OSM's features by combining extrinsic and intrinsic aspects, like [9], that evaluated the positional precision of OSM based on the combination of the edition's history. Besides that, the most recent researches have focused on comprehending spatial and temporal aspects of events in OSM contributions [10], as well developing add-ons for evaluating data quality, as is presented by [11], that developed a QGIS toolbox to evaluate parameters of the intrinsic quality of OSM features. 
The literature identifies as one of the main challenges for the integration processes, the heterogeneity of the data. Once the quality may vary according to the study area, the indicator used of even the spatial variations through time in the same region. In this context, to understand the adjustment of OSM's resources to the topographic mapping, it is crucial to connect aspects related to the quality and heterogeneity of data. Researches like [1] argue that, based on the obtained quality, the resources resulting from VGI may be used to integrate, detect changes or report errors. Therefore, classifying resources from OSM according to their usability in a certain region becomes essential, especially in developing countries like Brazil. Besides that, the research that explores issues of quality, heterogeneity, and contributions patterns of OSM is still not widespread in developing countries [12].
Given the importance to classify OSM features according to their usability for a given region, especially in developing countries, few researchers explore quality, heterogeneity, and contribution pattern issues of OSM in Brazil. we proposed a hypothesis that understanding aspects of the extrinsic and intrinsic quality of the quality of OSM features, related to spatiotemporal aspects of contributions in developing countries, will help decision making regarding the influence of the dynamics of insertion of features concerning quality.
 Thus, this research has as an objective to evaluate the extrinsic quality of OSM features for the county of Salvador-Bahia-Brazil (the northeast region of the country). Therefore, we investigated indicators of positional accuracy, thematic accuracy and completeness, the visualisation of heterogeneity of data, and the analysis of the edition history. To accomplish the evaluation of extrinsic quality, the OSM features were compared to the topographic mapping of the country regarding the Cartographic and Cadastral System of the County of Salvador (SICAD, 2006) and features from the Urban Development Company of the State of Bahia (CONDER).
The analysis of positional and thematic accuracy was made through procedures of feature sampling. The analysis of completeness occurred from comparing the total of available features. The verified categories were features from the road system, religious, educational, and health buildings. We divided the municipality of Salvador into sub-regions to identify different local patterns of quality in the analysis of thematic accuracy and completeness. The visualisation allows obtaining the data's heterogeneity through a plugin developed in the software QGIS, making the planimetric positional evaluation for point and line features. The statistical procedures for developing the plugins were realised based on the Brazilian law to evaluate geospatial data quality analysis [13] and based on the method of double buffer proposed by [14].