The calculated distance (air line) between San Luis Potosí and San Diego de la Unión is approximately 48 miles respectively 77 kilometers.
By car or train, the actual journey to San Diego de la Unión is certainly longer, as only the direct route (as the crow flies) between San Luis Potosí and San Diego de la Unión has been calculated here.
Air line (approximately)
77 kilometers
41 nautical miles