Notice how the sea floor slopes up as it approaches the shore on the starboard side of the image.
In the main window, a 3D image of the sea floor is shown with color mapped to depth. Note that the water is deeper to the port of the vessel. This corresponds to the chart. A bridge piling is just cominging into view at about 500m range. This is an example of the sonar operating with the wide, 90 degree field-of-view. The entire 3D image is generated with a single ping.
This image from a FarSounder forward looking sonar shows the sea floor mapped to nearly 14 water depths. Beyond the bottom mapping range of the sonar a bridge piling is detected in red. Reflections from a green marker buoy is detected slightly to starboard, about 170 meters ahead of the vessel.