These data come from NASA's Terra and Aqua satellites. Both satellites are part of the general Earth Observing System (EOS) network.
The locations of fires are determined by heat anomalies detected by the satellites. Having a satellite based method of detecting fires is valuable as it provides firefighters an advanced view of the current situation in nearly real time. This can save lives and property.
The size of the points corresponds to the "Fire Radiative Power" which is the power output of the fire in MegaWatts (MW).
The color of the points corresponds to the "Brightness Temperature" of the fire, or it's temperature in Kelvin (K). Colors chosen for legend represent the lowest and highest values seen in the dataset.