I too am curious. I'm surprised at how little information there is on the rather large DJI.GIS file that the Mavic Air has deposited on my SD card after recording video for several flights. GIS is the acronym for Geographical Information Systems and seems to be a reference to software/format that maps or encodes video imagery for use in such a system. However google has almost no information on the specifics of DJI.GIS or what application uses it. The size of the file suggests that it combines GPS geographical information with recorded video, but that just an educated guess.
I did open the file and it is a binary format, not text. A hex dump reveals that the header is "GIS". If I had to guess, it would be that it is a GIS file, but using some proprietary DJI format.I would surmise that it is storing flight tracks or some other form of location data; but I was hoping someone would know.