Port Visits

Which vessels visit the most ports, and which ports see the most traffic -- geofenced against port locations.

Geofence: 1km around each port's center · a visit needs at least 15 minutes' dwell to count (shorter dips, e.g. a vessel transiting a port's approach channel, are discarded as noise, not recorded at all) · bounded by the same 7-day vessel-position retention window as the rest of this app. Ports/vessels with zero visits in that window aren't shown. Regenerate via tools/build_port_table.py and tools/build_port_visits.py.