Zapiet - Rates by Distance calculates distance with the help of a route and address provider, also known as a geo provider. You can choose a provider in Zapiet - Rates by Distance Settings > Route and address provider. The ones you can choose from are:

We’ve chosen OpenCage as the default route and address provider because it requires no setup, and doesn’t cost you anything. Distance calculation will work out of the box.

While OpenCage works great for most merchants, sometimes you might want the pinpoint accuracy that only Google Maps and HERE can provide. You will, however, need a Google Maps and HERE API keys to get them up and running.

Google Maps and HERE provide free credit each month, and it most often covers the monthly cost. However, these providers will charge you if you go over their limit.