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Google Maps includes a one-handed zoom option. You double tap on the screen and drag a finger up to zoom in and down to zoom out. If you fancy reversing this, you're going to need to install this Xposed Module (bit.ly/1MO64lE).

Install the module. Once you’ve rebooted, head to Google Maps. Try a double tap and if everything's worked you now zoom in by swiping down and out by swiping up. if not, you might have an incompatible version of Maps.

If you want to change your settings back, just uncheck the box next to the module and then reboot. There are no other settings to tweak here. If you want to delete the module, long press it and then tap uninstall.