Lol! Yeah, I know. A lone seamount got in his way, but the overall general depth is known.
You're starting to catch on.
Depths for SURFACE navigation on much of the ocean ARE well charted, but the abyss and sea-mounts, if they are in an area of widely separated soundings, are not necessarily so.
Neither are the deeps, because no one goes there.
I have spent this time to point out that your "SHEESH!" post was inappropriate and uninformed (as opposed to politely curious and inquisitive).
See this NOAA Chart 531 and note there are commonly 40NM intervals between soundings. (takes a little while to load - pan and zoom at the upper left) )