OpenSeaMap – the alternative cost-free nautical chart

OpenSeaMap – the alternative cost-free nautical chart


Nautical charts are expensive and in many countries data are not always up to date. OpenSeaMap is an alternative cost-free solution, open for public worldwide.

Following the example of Wikipedia, the data are collected by crowd-sourcing. OpenSeaMap involves experienced mariners, programmers, and thousands of data collectors. All these volunteers are working to produce a nautical chart with comprehensive, relevant, and up-to-date data for water sports.

The web-based chart contains information on oceans, rivers, and topography. However, the chart does not end at the coast line but shows details about the harbour, the infrastructure of various places, traffic routes, and much more.

Until now, users of the nautical charts have usually been skippers and motorboat operators. However, growing numbers of divers, surfers, kayakers, anglers, and other water-sports enthusiasts are keen to benefit from OpenSeaMap, too.

Nautical information such as seamarks and nautical lights are shown on OpenSeaMap

A worldwide geo-database, made by the crowd

OpenSeaMap is part of OpenStreetMap. The collection of free spatial data works just the same.

There are three sources of data:

  1. One million enthusiastic cartographers who collect spatial data using GPS in their spare time.
  2. Authorities and organisations that increasingly embrace the idea of Open Data provide data voluntarily. For example, OpenSeaMap is allowed to use water level information and tidal information from Germany, Austria, and Switzerland.
  3. Aerial photos with partly excellent resolution obtained from Bing (Microsoft), local authorities, and organisations are manually transformed into vector data of spatial information.

Integrated information for skippers

The base map is rendered from OpenStreetMap and additional information is depicted in layers.

All in all, OpenSeaMap provides access to a wealth of information for skippers of sailing and motor boats. For example:

  • A ‘navigational aids’ layer contains typical features of a nautical chart. It has 18 zoom levels that range from a view of the world to detailed harbour plans in 1:2000 scale. The most advantageous combinations of objects are depicted for each particular zoom level.
  • A ‘harbour’ layer shows 6,000 harbours, thousands of marinas, and anchorages. Clicking on the symbol opens the harbour pilot, which can be updated by users with detailed descriptions and images of the harbours.
  • A ‘weather’ layer comprises weather maps of the world including parameters such as wind direction and wind force, air pressure, temperature, precipitation, and wave heights. Also included is a three-day weather forecast.
  • A ‘water depth’ layer shows the deepwater bathymetry by GEBCO.
  • A ‘ship tracking’ layer shows the AIS positions in real time.
  • A ‘Wikipedia’ layer has direct links to 3.5 million Wikipedia articles.

Offline charts are available for the use en route. They can be used with Android- and Windows-tablets, iPad, and Garmin Plotter

Sports layer for other water sportsmen

The ‘sports’ layer especially addresses other water sportsmen than skippers. Among other things, this shows great diving spots, diving schools, and places for filling up scuba tanks. Kayaking routes are marked with different colours depending on their degree of difficulty. Also clearly indicated are entry and exit points plus obstacles and spots where kayaks need to be carried.

Sports layer with swimming and diving spots

Special project: Measuring water depth by crowd-sourcing

Depth information is difficult to obtain from governments. That is why OpenSeaMap wants to measure the seacoasts worldwide using crowd-sourcing.

Most ships are equipped with GPS and sonar systems. The devices write the data via an NMEA string format. An NMEA data logger, which was developed specifically for OpenSeaMap, then stores the data on a USB stick. The collected data can then be transferred to the central server. The raw data can be corrected (fed with heel and tide data) and calculated to create a terrain model. From this, depth contours will be derived and shown in the chart.

The red lines are tracks from measuring water depth with the NMEA data logger

The OpenSeaMap community is big and spread all over the world, so chances for this ambitious project are rather good. However, there are other challenges such as feeding the system with tide and wave information data. It is therefore important to have bathymetry specialists contributing to OpenSeaMap.

Be part of the OpenSeaMap community!

If you are a developer, we would love you to join OpenSeaMap – we could use your experience in various fields such as servers, databases, rendering, hardware, microcontroller, web programming, app programming, graphics, web design, data transformation, statistics, geodesy, bathymetry, cartography, translations, and more.

Researchers and scientists can help OpenSeaMap feed the system with depth data. We are looking for tide models, waves, wave travel times, ship movements, etc. Professors and students alike can find exciting topics for diploma theses or internship reports.

Or you can help us update the chart with spatial information about your place of residence or home country and even by telling people about this project. Let’s build the chart together!

Contact [email protected]