I have not kept up with scanner capabilities since I left the Navy over 30 years ago and worked on some of their radio frequency scanners.

You might try a google search on radio frequency allocation or RF band plan

And, the FCC web site may have some of the info.

From what I have been reading, frequencies are allocated for commercial communications based on location. The main point would be to limit potential for interference within a normal operating environment.

And, there is a lot of frequency sharing happening in some areas.

The military has a number of frequencies that are allocated. As do public safety agencies.

I am trying to come up to speed on the latest changes in ham radio equipment.

Yeasu makes a good radio that covers 40 MHZ up through the 800 MHZ range.