- Sediment data from the USGS publication, usSEABED: Atlantic Coast Offshore Surficial Sediment Data Release (USGS Data Series 118) were augmented by seafloor sediment data from DMF lobster surveys, DMF trawl surveys, EPA/EMAP grab samples, MWRA grab samples and SPI data, National Coastal Assessment grab samples, and USGS Open File Reports. The data points were converted to Thiessen polygons to create a surficial sediment map, resulting in the following four categories: muddy, sandy, gravelly, and hard bottom. Note that the distribution of points in the aggregate dataset is not uniform -- this causes polygons to differ in size and shape throughout Massachusetts waters.
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