im researching on game navigation and path finding. I need some questions to be answered.

really navigation mesh is simply a A* behind it? just that? so navigation mesh is only places agent can go and only graph of empty objects that agent can move from one to another?

are grid A* so big that covers all the place or they are less?

is a matrix really good data structure to save info ofconnections and distance into them? for example calculating in every frame distance of every element of graph in matrix from player cat be very efficient.

im searching to use ACO algorithm in some part of my implementations for less predictablity and more realism. don't know it can be a good approach.

please give me some information you know about optimized implementation of navigation in games.

thank you for helping.