In the videogame Assassins Creed how does Desmonds mind fill in the spots that Alta�r didn't actually go?

Say Alta�r went to go assassinate a Templar, so Desmond must do the same, but Alta�r takes a route across the rooftops, and Desmond takes a route down an alley that Alta�r never even saw, does Desmonds mind fill in the blanks with what he thinks should be there? What about for other senses? Smell, Taste ect.!