The EMODnet World Coastline service includes:

• Satellite Derived Coastlines for European waters at different tidal elevations

• World Coastline, derived from OpenStreetMap (OSM)

Existing methods for surface water detection from multispectral satellite data use the fact that water significantly absorbs most radiation at near-infrared wavelengths and beyond. This fact makes it easy to detect clear water employing spectral indices, such as the Normalized Difference Water Index (NDWI). In EMODnet-Bathymetry, a NDWI algorithm is used to derive coastlines for the European waters and part of the Caribbean waters from satellite imagery. This in combination with a tidal model allows, to retrieved coastlines at different vertical datum (Mean-Sea-Level (MSL), Mean-High-Water (MHW), and Lowest Astronomical Tide (LAT)). Huge volumes of satellite data have been processed in parallel using a mixture of top-of-atmosphere reflectance satellite images from NASA/USGS Landsat 8 and ESA Sentinel-2 satellite missions, acquired during 2013-2020. For the correction for sea level variation use has been made of the Global Tide and Surge Model (GTSMv4.1) from Deltares, which provides instantaneous water level and tide levels with global coverage. More detailed information can be found in:

https://emodnet.ec.europa.eu/sites/emodnet.ec.europa.eu/files/public/EMODnet_Bathymetry_2024-satellite_derived_coastline_report_Deltares_Feb2025.pdf

The Satellite Derived Coastlines are available for download as shape files and included in the Coastlines map layer on the EMODnet Central Map Viewer, and included in the EMODnet Bathymetry OGC WMS service.

OpenStreetMap (OSM) is a collaborative project to create a free editable map of the world. The geodata underlying the map is considered the primary output of the project. The creation and growth of OSM has been motivated by restrictions on use or availability of map data across much of the world, and the advent of inexpensive portable satellite navigation devices. OSM is considered a prominent example of volunteered geographic information.

The land polygons describe polygons for all land areas in the world, ie. continents and islands. Optionally, large polygons are split into smaller overlapping chunks that are easier and faster to work with.

The data has been derived from OpenStreetMap ways tagged with natural=coastline. Ways are assembled into polygons and then split. Some errors in the OSM data are repaired in the process. Where polygons have been split they overlap slightly to help avoiding rendering artefacts at the seams.

The OSM derived world coastline is included in the Coastlines map layer on the EMODnet Central Map Viewer, and included in the EMODnet Bathymetry OGC WFS service.