For the best possible accuracy from your GPS (this goes for all brands) you want to mount the GPS Receiver where it will have an unobstructed view of the sky (blocking any satellite signal could lessen the position accuracy). To get the most accurate waypoint coordinates from objects seen on the sonar you need to mount the GPS Receiver as close to the transducer as possible. So the best location and installation would be back on the transom above the Si transducer but also on a pole or mast that places the GPS Receiver above the level of the motor. Most though just go ahead and mount the GPS Receiver on the gunwale or top of the transom as the pole gets in the way when fishing.