Someone should make a list of these undocumented keystrokes, some of the best features are hidden there (eg I just dicovered CRTL F1 - F4)
This one was documented:
Page 23 of the manual: "It’s possible to see what the structures in a region are by doing a Ctrl-click on the structure sprite."
Page 24 of the manual: "Industrial Structures: These are located inside cities (see Summary in the Appendix). To see them, use Ctrl-click on a city sprite. They will then be displayed inside the Stack Panel."