You can easily adjust the voice navigation volume in Maps up or down while using the navigation app by pressing the volume buttons on the side of your iPhone. But you probably don't want to discover you can't hear the voice navigation in Apple Maps and then have to mess with your phone while you're barrelling down the highway. A safer way to make sure the voice navigation is always at the right volume is to change Map's default volume.
You can change the default volume from within the app itself or from within Settings.
To change the default volume from within Maps, enter your destination and tap start. Next tap anywhere on the navigation screen and then tap on the volume icon that appears in the lower right corner. Select the default volume you prefer from the menu.
To change the default volume from within Settings, go to Settings>Maps and choose your preferred default volume setting.
In Maps Settings you can also choose whether you see distances in miles or kilometers, turn off English as the default language for map labels, and choose whether the app offers walking or driving directions as a default.
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