Chart 5101A, first published in 1939, showing contours to be used for contour- following navigation

Chart 5101A, first published in 1939, showing contours to be used for contour- following navigation. This was the first chart produced by the C&GS and among the first in the world to have adequate bathymetry for use by mariners as a navigational tool. The data was acquired in the 1930’s as the result of radio- acoustic ranging surveys allowing precise positioning far from shore.

Photo Location: California,