Just like another gentleman put it, when you are talking about analogue or digital migration, what they are talking about is about (signal) transmission of Data. Not the format of the data (content). In summary, Analogue is synonymous with continuous waves while Digital Transmission is bits ie 0s and 1s.
In full:
Analog Transmission
Continuous/constantly changing - characterized by waves and signal loss
Digital Transmission
Defined by discrete values ie 0 from 1. 0 - low voltage | 1 - high voltage
The world is moving towards digital to free up frequencies (analog has very many overheads) that can be taken up for other uses.
To confuse you... Digital signals really are Analog signals - where the voltage levels over time have special meanings! Haha! - Physics humor...