the way II/infinitive vs. gerund

[navi tasan]

Which are correct:

1-The only way to find out where we are is to look at the map.
2-The only way of finding out where we are is to look at the map.
3-The only way to find out where we are is looking at the map.
4-The only way of finding out where we are is looking at the map.

[Horsa]

As far as I'm concerned 1 and 2 are OK.

If you add 'by' to the others, they would be OK too.