Why moving a base

As the base size grows you may wish to kill outposts that match the size of the base. Also, you need to secure POI's (to gain bonuses) and move towards the centre (to kill the fortress).

Thank you!! Understood.
I only can move 20 fields. So it will take a looot of time to get near to the centre.
How often am I able to move?

How often you are able to move will depend on the size of your construction yard and how much cooldown period you get. This gets bigger as the base grows. You need to join a training alliance where many of your questions can be answered quickly.