What is Mapsource and why do you need it for the T4A GPS Maps?
Mapsource is an application which enables you to view Garmin compatible maps on your PC, do route planning and transfer maps, waypoints, tracks and routes between your PC and your Garmin GPS device. T4A GPS Maps are Garmin compatible maps and you need Mapsource to view it on your PC and to transfer it to your Garmin GPS device.