This formula may help. But it can't find the nearest coast. Perhaps you could put the formula with set of coastal locations into a spread sheet along with the properties so set of distances for each property could be seen. https://en.wikipedia.org/wiki/Haversine_formula
answered
andy mackey |

There has been done quite some research on finding places that have the largest distance to the nearest road/coast/settlement etc: Pole of inaccessibility. To do that you basically need to answer the same question you have. Maybe that gives you a hint on how to expand your search.