A party can move a child away from the other if there is a Separation Agreement or Order allowing them to do so. If there is not, then the other party can start a court Application and bring a motion to keep the child in the area. A court will usually look at the history of the parties, who makes the decision, where the child has lived and the reasons for the move, among other items.
A party who wants to move out of the jurisdiction should either get a court Order or a written Separation Agreement before they start making plans to move.