Diggability maps are based information from the maps Sediments (grain size) and Sediments (genesis). The map tells you how easy it is to dig into the seabed.
Diggability map for the Astafjord area (www.ngu.no).

This map is based on bottom type and provides information on how diggable the bottom is, and about the expected stability of the sediments that may be dug out. While it might be very difficult to dig in a seafloor of glacial till which contains cobbles and boulders, a bedrock seafloor may require blasting. The map is important during the planning phase, for example, planning for pipelines on the seafloor and finding suitable sites for oil platforms  and other submarine installations.