Deriving POI for the Cape of Good Hope.

The blue area inside the quadrilateral is centered at Cape Town, South Africa edge to center is around 1,000 km. The area is divided into H3 indices with resolution 3. Each index is colored according to the distribution of AIS message with the darkest as the index with the highest frequency. The green H3 indices at the center represent the hexagons selected for the Cape of Good Hope polygon (see inset).