  We reconstruct the temporal evolution of the source distribution for the four
major gas species H2O, CO2, CO, and O2 on the surface of comet
67P/Churyumov-Gerasimenko during its 2015 apparition. The analysis applies an
inverse coma model and fits to data between August 6th 2014 and September 5th
2016 measured with the Double Focusing Mass Spectrometer (DFMS) of the Rosetta
Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) and the COmet
Pressure Sensor (COPS). The spatial distribution of gas sources with their
temporal variation allows one to construct surface maps for gas emissions and
to evaluate integrated productions rates. For all species peak production rates
and integrated productions rates per orbit are evaluated separately for the
northern and the southern hemisphere. The nine most active emitting areas on
the comet's surface are defined and their correlation to emissions for each of
the species is discussed.
