Horizontal Accuracy Tests on Google Satellite Images Over Naples Added in QGIS

The possibility of view Google satellite images in Geographic Information System (GIS) provides an important source of information for free to support applications regarding smart cities. In fact, Google makes available, practically for every place on Earth, updated and high-resolution images: it is necessary to ascertain that the data accuracy is compatible with the application you want to create. Consequently, it becomes necessary to verify that the coordinates of objects easily identifiable in the images are sufficiently accurate for the purpose. This article aims to verify the horizontal positional accuracy of the Google satellite images in the municipality of Naples (Italy). For this purpose, the 1:1,000 scale maps georeferenced in the UTM WGS84 system, zone 33 North are used. The satellite images, georeferenced in the WGS84 system and in the WEB Mercator representation, are also reported in the same system and projection as the maps. Due to the imperfect overlap between the layers, the deviations are measured in some points that are easily identifiable both on the maps and the satellite images. As found with the use of 45 check points, the deviations have a root mean square error (RMSE) of 1.594 m highlighting a wide range of possible applications.