The Open SeaMap Project heads to sea

Drawing on the efforts of GPS-carrying volunteers to create worldwide navigational charts accurate enough to use on the open water, a group of nautical enthusiasts and amateur mappers are seeking to do for sea charts what the OpenStreetMap is doing for road maps and city streets,

This project calls for a need for precision that goes much more than that of a street map. However, supporters of the project are convinced they can do better than the myriad of maps already in existence that are emblazoned with the warning “Do not use for navigation.”

The Open SeaMap Project
Sea mapping is a vastly different entity altogether than mapping roads and city streets.

To be of use the charts need to contain information about lighthouses, water depth, harbours, invisible undersea objects such as sand bars or sunken ships, all mapped with extremely accurate navigational coordinates.

Some of this information is in existence already without the volunteers having to gather it entirely from scratch. Currently work is being carried out on translating a list of known lighthouses around the world into the database. But volunteers must ultimately check even this information, as it is frequently no longer accurate, or was never quite correct in the first place.

Other aspects are much more difficult. Depth readings, for example, must be taken with reference to a specific reference sea level, since tides and weather ensure that the apparent sea level varies widely over time. There are several ways of doing this, referring to levels such as the mean low water or the lowest astronomical tide. This requiring that volunteers either settle on a standard, or ensure they describe their depths relative to a known – and specified – level.

Even something as familiar as longitude and latitude coordinates can be deceptive. Map systems from various countries use slightly different reference models of the shape of the earth to ground the familiar coordinate points most of us are used to hearing. The difference in these models mean that the same coordinate points might be a few hundred metres away from each other on different maps.

The project is in its very early stages, with some work evident on the coastlines of Germany and the United Kingdom. They’re still looking for sponsors, technical and mapping volunteers, and ideas.

For sailors who have always imagined a bit of Magellan in themselves, it’s certainly a project to watch.