By default, the detection process applies a contour interval, between a minimum and maximum depth, at value equal to half the resolution of the surface.
For instance, if a surface has a min/max depth of 5/40 metres, with a resolution of 1 metre, the process will contour from 5m to 40m at every 0.5m, resulting in contours at 5.0, 5.5, 6.0 …, 39.5, 40.0.
You can optionally set a specific value as the contour interval, or use a levels file. Contour levels files, or depth list files, are text files that contain a list of specific depths for contouring data. In a level file, values are negative when representing heights above the datum, and positive when representing depths below the datum. See Depth Range Files for an example.