Yesterday, a paper was published in Science on the creation of new, higher resolution maps of the ocean floor using gravity anomaly data collected via satellite. The authors write, “at scales smaller than 200 km, variations in marine gravity primarily reflect sea-floor topography.” Since rock has a different density than water, precise gravity measurements allow for an estimation of ocean depth. One of my first thoughts was to use this data in a map.
The authors provide their data for download; however, it is provided as GMT grid files, which are apparently common for oceanography research, instead of something more standard for GIS such as GeoTIFF. Using GMT, I was able to convert the data to the GDAL supported NetCDF format, although I had to reencode the file with CDO before GDAL would handle it. Using GDAL, I then reprojected the data in EPSG:3857, converted it from floating point to integer, and created a GeoTIFF file to be more friendly to web mapping applications.
Since Mapbox Streets doesn’t include a layer for land, I masked out land masses from the gravity anomaly map with Natural Earth’s 10m land polygons in TileMill and created tiles down to zoom level 7. Below, the tiles are displayed using Mapbox GL JS with a slightly modified outdoors style (if the map displays as a solid color, try clicking and dragging).
Download the GeoTIFF Marine Gravity Anomaly Map (417 MB).
Also, a 32-bit floating point version (3.5GB), and a 32-bit floating point GeoTIFF of the vertical gravity gradient map (3.5GB).