"Here’s how to do it. Zoom in on a part of a map that you want to save for offline browsing. Then, tap the search bar and type “OK Maps” (minus the quotes) and hit the Search button. You can also speak this into the phone — just speak “O” and “K” with a slight pause between them, otherwise your phone may spell it as “Okay” and this trick won’t work.
If all goes well, you should see a prompt indicating that the map is downloading. It will take about 10 seconds, depending on the size of the map you’ve selected and the speed of your internet connection. Wait for the message that says “The on-screen map area has been cached,” and you’re good to go.
The next time you open Google Maps and there’s no signal available, you’ll be able to view and browse your saved map. It’s especially helpful on Wi-Fi-only iPads or Android tablets, and for when your device is in airplane mode. For example, you can virtually explore the area around your hotel while you’re flying to the city you’ll be visiting. And speaking of foreign travel, this is also very helpful for exploring cities where data roaming is excessively expensive and public Wi-Fi spots are rare."