In order to identify geologic features of sea floor, it is important to be able to read and understand bathymetric maps so that we can better interpret the features that we see. Bathymetry is a map making concept that is used to portrait the depth to the bottom of the ocean and thereby provide information about the 3 dimensional shape and location of ocean floor landforms. Many different techniques have been used to measure ocean depth including weighted lines, side scanning sonar, gravity and even sea surface height measurements. These maps are similar to topographic maps of the continents in that they show locational information, together with the third dimension of depth, thus giving the user a sense of the distribution and dimensions of various sea floor features including mountain ranges, canyons and plains. Bathymetric maps can display depth by color shadings or more commonly by using bathymetric contours.
Contours are lines that represent regions of equal depth of the sea floor.
Index contours are labeled with numbers that represent depth. Not all contours are labeled, so a contour interval is usually listed on the map to indicate the vertical depth change between each successive unlabeled bathymetric contour. The pattern of contour lines on a bathymetric map help in interpreting the sea floor landforms. For example, closely spaced contour lines indicate a steep hill side, whereas as widely spaced contour lines indicate a flat bottom. Bathymetric contour map of a portion of the sea floor Artist's sketch of the seafloor based upon bathymetric map from above.