Almost two decades now, and I never found this out.
Even a hotkey FAQ doesn't help.
At the start of a turn, I get a message "something awful happened at/near <city name>.
I only ever play huge maps - how do I find <city name>?
Indeed, when messages about events are displayed, there is no possibility to switch to the map, you can only view the base/city itself.
However, after the messages are shown, and the player makes their moves, Ctrl + B invokes the Locate Base window.
One possible trick I personally like is renaming the bases (cities), prefixing it with continent name/number/id/whatever. This also helps alphabet-sorting the bases (cities) and navigatiion with Left/Right arrows between them, as shown in the screenshot (caveat: IIRC, the list was unsorted in SMAC and fixed only in SMAX).