Bathymetry: Mapping the Land Under the Water

There is as much landscape under the water as above it — ridges, slopes, basins and banks — and bathymetry is the study of it. The word covers the beds and floors of every kind of water body: the ocean, and rivers, streams and lakes too.

A bathymetry map of East Flower Garden Bank. Credit: NOAA.

From depth to shape

At first, "bathymetry" meant only one thing: how deep the ocean is compared with sea level. Over time the meaning grew to "submarine topography" — not just the depth of the water, but the shape of the terrain beneath it.

A topographic map, turned upside down

A bathymetric map does for underwater land what a topographic map does for dry land: it shows three-dimensional relief on a flat page. Mapmakers use color and contour lines to show how the sea floor rises and falls. Those underwater contour lines have their own names — depth contours, or isobaths.

The foundation of hydrography

Bathymetry is the base on which the wider science of hydrography is built. Hydrography measures the physical features of a body of water, and it takes in much more than the bottom:

Sources

Based on "What is bathymetry?" from NOAA's National Ocean Service, a work of the United States government in the public domain.