To access this Google feature, iOS and Android users must update to the latest version or download the latest Google Maps version for their devices.
You can download Google Maps for iOS here or Google Maps for Android here.
Open the Google Maps app, select 'Profile' next to the search toolbar at the top of the screen (Image below).
Scroll down to find the offline map section, choose 'Save map to use offline' to view maps when your device lacks Wi-Fi or 3G connectivity. (Image below)
Here, customize the map size to your liking and click 'Save' to have the application store it on your device. (Image below)
https://Mytour.vn/google-maps-offline-navigation-on-ios-and-android-86n.aspx
Note: With this new feature, the app will store information for a maximum of 30 days and then automatically delete it to free up device storage for you.
