A bathymetric chart is the submerged equivalent of an above-water topographic map. Bathymetric charts are designed to present accurate, measurable description and visual presentation of the submerged terrain.
In an ideal case, the joining of a bathymetric chart and topographic map of the same scale and projection of the same geographic area would be seamless. The only difference would be that the values begin increasing after crossing the zero at the designated sea level datum. Thus the topographic map's mountains have the greatest values while the bathymetric chart's greatest depths have the greatest values. Simply put, the bathymetric chart is intended to show the land if overlying waters were removed in exactly the same manner as the topographic map.
A bathymetric chart differs from a hydrographic chart in that accurate presentation of the underwater features is the goal while safe navigation is the requirement for the hydrographic chart. A hydrographic chart will obscure the actual features to present a simplified version to aid mariners in avoiding underwater hazards.
Bathymetric surveys are a subset of the science of hydrography. They differ slightly from the surveys required to produce the product of hydrography in its more limited application and as conducted by the national and international agencies tasked with producing charts and publications for safe navigation. That chart product is more accurately termed a navigation or hydrographic chart with a strong bias toward the presentation of essential safety information.
Bathymetric charts can also be converted to bathymetric profiles.
Free Bathymetric Chart OpenSeaMap
OpenSeaMap shows a worldwide bathymetric chart. From 10,000 meters to 100 meters, in low zoom levels in 23 blue coloured steps and a hillshade, and in high zoom levels with depth lines.  Data from GEBCO.
"Waterdepths by crowdsourcing" is a OpenSeaMap-project to measure shallow water depths between 0 and 100m, offshore and inland. Recreation skippers and commercial shipping, divers ans fishermen collect water depths with sounder and GPS. Measured tracks are showed in the chart.
Tools for generating bathymetric charts
- Generic Mapping Tools
- A freely available set of tools for generating any type of map, but originally and most commonly used for generating bathymetric charts
- 3-D Bathymetric Chart Activity: An introduction to the Nautical Chart
- "The very earliest rendition of a bathymetric map of an oceanic basin. Matthew Fontaine Maury published this map in 1853 in his book "Explanations and Sailing Directions to Accompany the Wind and Current Charts ...." NOAA Photo Library.
- General Bathymetric Chart of the Oceans (GEBCO)