Postal code distance calculator

Distances are great-circle: the shortest line over the Earth's surface, not a road or flight path. A postal code resolves to the dataset's representative point for the code, not an address, so a city-to-city figure can sit tens of kilometres from what a map route claims. Nothing is sent to a geocoder; lookups run against a bundled dataset in this tab. The bundled starter set carries a handful of sample rows per country, not the full GeoNames export, which the page credits under CC BY 4.0.