That is certainly possible. You can simply continue searching for and viewing locations. The download will continue as normal. When you return to the Downloaded countries overview, you will see that the download has been completed, or that the percentage has increased.
Please note: with an iOS device, it is important that you do not exit the app during the download process. If you do, there is a chance that the device will close the app and your download will fail.
Do you have an Android? Then the download will continue to work even if you use another app or lock your phone and put it away.