The numbers represent depth data at that specific point. We also include shipwrecks, sea grasses, navigation channels, spoil areas where dredging the Intracoastals and other channels are placed. The spoils actually get filled up toward the surface. The designation of their area is for navigation warning – it does not mean the whole area is full. It simply denotes the allowed area for the dredge. We show them reversed to point out the borders.
This data is collected from multiple sources including local captains, NOAA, USGS, US Coast Guard, CIA World Databank, Army Corps of Engineers, National Geophysical Data Center, the Environmental Protection Agency and each state’s and county’s GIS divisions.