What people on this board don't seem to realize is that there is also a turbine map. The turbine map depicts the turbine efficiency vs a mass flow parameter and the expansion ratio. It get a little more complicated because there is a range of efficiencies for a given shaft speed. The compressor is carefully matched to the turbine so that the turbine produces the best possible efficiency for a given mass flow and expansion ratio.
The reason no one looks at a turbine map is that it's really trivial for the end user to do so. The end sizes the unit using a/r ratio, trim and max speed of the turbine at a desired compressor output (which conveniently appears on the compressor map). Looking at the map that you posted, what could we understand that those three things don't already tell us or how that map overlays a compressor map?