Why is there PTH in the ground plane?

i have seen GPS Rx ckt having PTH in the ground plane can anybody tell me

theory of PTH .

is there any alternative for PTH

PTH's (plated through hole) in a ground plane are used to get a low inductance path to ground from another ground plane on the board, component ground, etc. Several PTH's are often used in parallel as this will significantly reduce the total PTH path inductance.