this is one of the most commonly used representation.
Let us say, let me put it in more simple terms as far as we are concerned as a user, we do not worry about how oceanographers have collected the data; we assume that they have collected the data that they are given as a spectrum, and our job would be to use in appropriate spectrum and then tell that look my ship should be capable of operating in up to sea state 3 or 4 or 5 this is a typical spectrum.