I just spent a few days in Italy, on the Ligurian coast. Even though we were on the west side of Italy, the Mediterranean sea was to the east, because the house was situated on a long bay. But zooming in even more, there were parts of the coast that were even more twisted — to the point where it had turned a full 360 degress so you ended up having the sea to the west again.

Erik Bernhardsson

A fun exploration of coastline geometry using OpenStreetMap data and trigonometry to find the world's most 'twisted' coastline segments. The author converts lat/lon coordinates to 3D unit vectors, computes cumulative exterior angles along coastline polygons using cross products and arc-sine, and ranks locations by total angular deviation. The top result is near Tauranga, New Zealand, followed by South Australia and Cape Cod, MA. The analysis notes that coastlines are fractal, so resolution affects results, and the maximum twistedness observed was roughly two full turns (4π radians).

Fun with trigonometry: the world's most twisted coastline