Monday, July 01, 2019

The Flashing Lighthouse Map

Lights at Sea is an interactive map which shows the location of lighthouses around the world. The map uses different colored flashing markers to show the light characteristics of each lighthouse shown on the map.

Individual lighthouses can have unique light characteristics so that mariners are able to identify them and use them as an aide to navigation. These light characteristics are created by using different colored lights, frequencies and light patterns. On OpenStreetMap these light characteristics are recorded using the tags 'seamark:light:sequence' and 'seamark:light:colour'. Lights at Sea uses these tags to show the color of lights and the light sequences used by the individual lighthouses.

The range of light emitted by a lighthouse is measured by how many nautical miles away it can be seen. In OSM the range of a lighthouse can be assigned using the tag 'seamark:light:range'. I assume that the size of the lighthouse circular markers on the Light at Sea map is being used to indicate each lighthouse's range.

One thing that is very striking on the map is the huge number of lighthouses in Europe compared to the United States. Norway in particular seems to have an inordinate number of lighthouses. According to Wikipedia there are actually less than 155 operational lighthouses in Norway. OpenStreetMap, however, seems to have plotted many more lighthouses than that on the Norwegian coastline. This is presumably the work of Slartibartfast.

One thing not shown on the individual map is the 'daymark' patterns used on individual lighthouses. Just as lighthouses can have individual light characteristics to aide maritime navigation they can also have unique 'daymarks' which enable mariners to identify individual lighthouses during the day. Daymarks often consist of large colored painted stripes, diamonds or other patterns.


Paul said...

I too was flabbergasted by some of the data - turns out it's not lighthouses at all, but beacons (of which lighthouses can be considered one type). That'd explain Norway to some extent, but in poking around a bit this afternoon it seems to be very incomplete - definitely more beacons in the US and Canada than what are displayed... More data at and

Anonymous said...

i'm currently modifying points, in france, from "lighthouse" to "lateral_beacon" :)

surfmadpig said...

I know of at least one operational lighthouse that's not on there (Happisburg, Norfolk) so Paul's explanation above sounds more and more plausible.