Since 1999, New York City’s Office of Emergency Management, charged with coordinating all aspects of the response, had occupied permanent headquarters in Seven World Trade Center, on Greenwich Street, just north of the landmark twin towers. A vital communications link was the radio repeater system based on the ground floor of One World Trade Center, the north tower. The loss of those facilities – and key personnel working there – significantly hampered the response.

<https://theconversation.com/disaster-communications-lessons-...>

<https://www.computerworld.com/article/2510996/9-11--top-less...>

I seem to recall an instance (I thought it was the NYC OEM, may have been another) in which both primary and secondary data archives were both within the WTC complex. Best practices now are to locate secondary / backup services at least 100--200 km from the primary. Preferably within different watersheds, seismic regions, etc.

Widespread disasters are comparatively rare, but can affect considerable areas, and locations sufficiently proximate might well be affected.