A computer-implemented method for validating and monitoring a performance of a Global Navigation Satellite System, GNSS, receiver to detect interference or spoofing, the method comprising: receiving, by the computer (100, 1000), electronic diagnostic information from the GNSS receiver, said diagnostic information comprising a plurality of observations at different times of signal strength of one or more satellites at each point in a visible sky; building, by the computer (100, 1000), a flat map of the visible sky using the received diagnostic information, wherein the flat map includes a track of the one or more satellites; calculating, by the computer (100, 1000), for each point in the visible sky of the flat map, an aggregated signal strength of the one or more satellites over a predetermined interval using the received diagnostic information; generating, by the computer (100, 1000), a heat map over the flat map of the visible sky and the calculated aggregated signal strengths; displaying, by the computer (100, 1000), a visualization of a flat heat map on a graphical user interface of a display device, the flat heat map comprising the generated heat map over the flat map of the visible sky; storing, by the computer (100, 1000), the diagnostic information and the flat heat map in an observation database; based on the stored diagnostic information and the flat heat map in the observation database, analyzing, by the computer (100, 1000), the aggregated signal strengths of the one or more satellites in the flat heat map to detect one or more problems with the GNSS receiver; and generating, by the computer (100, 1000), an alert if the one or more problems are detected in the flat heat map to indicate interference or spoofing. receiving, by the computer (100, 1000), electronic diagnostic information from the GNSS receiver, said diagnostic information comprising a plurality of observations at different times of signal strength of one or more satellites at each point in a visible sky; building, by the computer (100, 1000), a flat map of the visible sky using the received diagnostic information, wherein the flat map includes a track of the one or more satellites; calculating, by the computer (100, 1000), for each point in the visible sky of the flat map, an aggregated signal strength of the one or more satellites over a predetermined interval using the received diagnostic information; generating, by the computer (100, 1000), a heat map over the flat map of the visible sky and the calculated aggregated signal strengths; displaying, by the computer (100, 1000), a visualization of a flat heat map on a graphical user interface of a display device, the flat heat map comprising the generated heat map over the flat map of the visible sky; storing, by the computer (100, 1000), the diagnostic information and the flat heat map in an observation database; based on the stored diagnostic information and the flat heat map in the observation database, analyzing, by the computer (100, 1000), the aggregated signal strengths of the one or more satellites in the flat heat map to detect one or more problems with the GNSS receiver; and generating, by the computer (100, 1000), an alert if the one or more problems are detected in the flat heat map to indicate interference or spoofing.