Use of Geometry in Search and Rescue Planning - Perpendicular Bisector

Lew W.S.
In search and rescue operations, search teams need to plan how to conduct the search. In the example below there are two search teams, one at Mersing and another at Kuantan and they were looking for two missing persons in the South China Sea off the east coast. How will the teams divide the area of search in the sea? Use the slider to show the presentation.

What was the perpendicular bisector used for in this situation?