pad method
Implementation
void pad(double bufferRatio) {
var heightBuffer = (_sw!.latitude - _ne!.latitude).abs() * bufferRatio;
var widthBuffer = (_sw!.longitude - _ne!.longitude).abs() * bufferRatio;
_sw = LatLng(_sw!.latitude - heightBuffer, _sw!.longitude - widthBuffer);
_ne = LatLng(_ne!.latitude + heightBuffer, _ne!.longitude + widthBuffer);
}