Well, they start in okinawa, actually. As spring progresses, the line moves up to honshu (the main island) and finally up to hokkaido. They have daily sakura forecasts on the news showing exactly where is in bloom and predictions for other places. So the celebration begins at different times in every city. City officials usually have a pretty good idea when they will bloom based on previous years, but they always consult the sakura forecast before scheduling the sakura festival.
There is a hill somewhat near Kyoto that is the source of the wild ancestor to what is the most popular cherry tree today, and that hill is completely covered. That could be what the TV show you watched was referring to. It looks amazing. Search "mount yoshino cherry blossom" in google images to see some amazing photos of it.
I didn't know that, that is pretty cool, also kinda crazy that there are things such as sakura blossom forecasts!