Geoprocessing of data records

We applied geospatial and geometric operations to check and correct the raw data collection. This geoprocessing was performed to avoid double counting of mining areas, correct invalid geometries, and add attributes (variables) to the polygons. To avoid double-counting, we dissolved polygons that possibly overlapped or shared a common boundary, i.e., we merged them to form a single polygon. After that, we removed sliver polygons (unwanted small polygons) and invalid polygon geometries, producing a consistent set of polygons.

From this set of preprocessed polygons, we calculated the area of each feature and added information on the country where each polygon is located. We calculated the area in square kilometers by projecting each polygon to its respective Universal Transverse Mercator (UTM) zone. After that, a spatial join query acquired country name and ISO 3166-1 alpha-3 code from country’s administrative units geometries available from EUROSTAT³⁸. The final set of polygons thus includes the geometries (polygons) covering the mining areas, their respective areas in square kilometers, country name, and ISO 3166-1 alpha-3 code of the corresponding country.

From the mining polygons we derived global grid data sets with the mining area at 30 arcsecond, 5 arcminute and 30 arcminute spatial resolution (approximately 1 × 1 km, 10 × 10 km and 50 × 50 km at the equator). This is useful because many modeling applications require standardized grid data³⁹. The 30 arcsecond grid was derived from the percentage of area of the geometric intersection between each cell and the geometries of the mining polygons. These percentages were rounded to zero decimal digits to reduce the size of the data set. Therefore, the percentage of the cell covered by mine should be greater than 0.5% to be considered, i.e., approximately 0.5 ha at the equator. To obtain the gridded mining area, we estimated the area of each cell in square kilometers and multiplied with the percentage of mining cover per cell, resulting in a 30 arcsecond global grid indicating the mining area within each cell. The 5 arcminute and 30 arcminute grid resolutions were downsampled form the 30 arcsecond grid. All scripts used in the geoprocessing of data records are available with our open-source web application tool³⁵.