Checking this option will scale the size of the map icons at tracked location points according to the ocean depth at which they were collected: points nearer the surface have larger icons while those measured deeper have smaller icons. In addition, the lines connecting successive tracked location points will vary in width according to depth as well (deeper is more narrow). Together these stylistic devices are used to provide depth perception for three dimensional trajectories such as profiling gliders.
with depth scaling (color-coded by water temperature):
without depth scaling: