Yup this is a nationwide issue. Some stations will stop broadcasting altogether. Some will not be affected at all. But just under 1000 stations will be changing the physical frequency that they broadcast on. However, because ATSC provides virtual channel numbers, the channel you know a station by will most likely not change.
It's tough to imagine how much spectrum was originally set aside just for over-the-air TV broadcasting in the USA. Channel 1 was lost a long time ago. Next went channels 70-83. Then channels 14-19 are "shared" in major cities like L.A. and N.Y. Channel 37 was given to radio astronomy. In 2009 channels 51 to 69 became the 700 MHz band.
This latest round "gives away" channels 38-51. The stations broadcasting on those channels will now either go off the air, move to a lower channel, or "share" a channel. ATSC makes it possible for multiple programs to be broadcast on the same physical channel.
A new over-the-air digital TV standard will also come with this change. ATSC 3.0 will allow broadcasters to cram more channels into the same 6 MHz channel space. In Chicago, for example, the NBC and Telemundo stations will be sharing over-the-air channel 33. Each will broadcast one 1080i (HD) and one 480p?(lower resolution SD) signal. For folks who watch TV using an antenna, this will mean you'll need to buy a converter box (external tuner) or a new TV. It's unclear to me if all stations will be required to switch to the new standard or not.
It's going to be a mess. It's good in the end, moving to h.265 and other modern compression schemes instead of stuff that was obsolete before they even started. It offers a "bootstrap" system that can tell the TV set what's going on without the user having to re-scan for channels. But the new system will be OFDM versus the current 8VSB so yes we're back to using converter boxes for a while. And they'll be expensive. The old converters were cheap because they only needed to provide SD analog outputs. In fact they were about $20 more expensive than they should have been on account of the stupid government coupon program.
As I understand this is a voluntary thing to begin with. Some broadcasters will jump right in to offer 3840x2160 resolution at 120 frames per second. Others will not want to spend a cent. At some point the government will likely require it putting an end to the current system. The idea being once some arbitrary percentage of consumer adoption of new gear is met they'll establish a deadline.
The plan is to get broadcasters (or one company with more than one signal) to group the old together on one channel and the new on the what would be vacant channel. They can do this without changing channels.
The channel change bit is related to the spectrum auction. The FCC is attempting to take another 100 MHz from broadcast TV so the band ends at 600 instead of the current 700 MHz, (compared to the 890 MHz the band once ended at). That means stations have to move, group, or go off the air.
The first thing over-the-air viewers will notice is that a channel they've been watching is no longer there. A rescan should hopefully find their new frequency, but as mentioned earlier, the virtual channel will likely be the same.
If/when broadcasters move to OFDM it will be a mess.