Due pinout diagram

Hardware Arduino Due
121

Nobody seemed to have asked these questions before, so I'll ask it now:

  1. Why do all pins have a "Digital Pin" and "Physical Pin" and "Port Pin" alias? Where are these aliases used to refer to these pins - for instance, when would I need to refer to pin A3 by A.22, or AD4, or D57, or 81?
  2. There seem to be many Reset pins. What does the Reset pin in the SPI cluster reset?