Within the Mileage module, we have a functionality to generate the distance between locations that are entered on the mileage lines and this is calculated via Google Lookup.
This can be turned on or off via:
Administration > Company > Settings > Expenses > Expense Settings > Use Google address lookup
Please note: The distance is being pulled directly from Google. We do not have any influence on the distance that is generated when the locations are entered on a mileage line.