A map shows the measurements taken for a given situation at a given point in time. In fact, external factors, which cannot all be taken into consideration, can affect the measurement.
The data shown on the map use the coordinates of a geolocation system. The precision of this data will vary depending on the quality of the GPS signal received.
Measurements can be affected by the presence of radioactive sources, which are not representative of the ambient radiological background noise: radium alarm clocks, patients or individuals having recently a nuclear medicine exam, etc.
Finally, it is important to remember that Geiger counters only measure gamma radiation, and not alpha or beta radiation and neutrons, which require other types of measuring devices.