This weekend we did a lot of driving around areas where we’ve never been before. I use Google Map for my navigation including the OK Google voice search from the lock screen for ease of use.
As I tend to view Google Maps with the satellite layer it comes on when using navigation.
Yesterday I got my bill from Vodafone, and whilst logged in I took a look at my current usage and it said:
Data 1.16 of 4GB used
You’ll get a new allowance on 16 Nov 2015

This meant in four days I used over a gig of data, checking my data usage within the phone it showed that 0.96GB of that was from Google Maps.
Fortunately I tend to use less than 2GB a month, so the exta gig on top is still below my allowance, but a note to self for the future, make sure tha satellite layer is turned off before navigating.