Do not stop the transfer.
Before you start a transfer, make sure there is enough memory available on your device or memory card for the data you want to transfer. Check the Total selected field for the amount of data you are about to transfer. On the line below, you can see how much memory there is left on your mobile device or memory card.
If you try to export huge amounts of data, such as the map of an entire country or continent, it may take very long until all maps have been transferred to the memory card. You also need to keep the USB connection to your mobile device and the connection from your PC to the internet on while transferring maps.