DEM

 A DEM map is what is known as a digital elevation model.  These DEM maps allow the people looking at them to visualize the elevation of the land.  These DEM maps only represent height information without any further definition about the surface.  This means that from these DEM maps you learn nothing about what is on the land such as houses or roads, rather just the elevation of the land.  The above DEM map is of the Great Barrier Reef, the Coral Sea, and the neighboring Queensland coastline, one of the many, many places I dream to scuba dive before I die.

The map URL is: http://e-atlas.org.au/content/gbr-jcu-bathymetry-gbr100