A graph showing the relationship between temperature and salinity as observed together at, for example, various depths in a water column. A T-S diagram for a given station is typically prepared by plotting a point for the temperature/salinity combinations at a range of depths and then joining them by straight lines in order of depth. The resulting line is called the T-S curve. Isopleths of constant density are often also drawn on the same diagram as a useful additional interpretation aid. In the ocean certain T-S combinations are preferred which leads to the procedure of identification via the definition of water types and water masses and their distributions.