Figure 4.7. Maps of seafloor topography (upper left) and backscatter intensity (upper right) in Nahant Bay and approaches. Both maps are overlain on NOAA-NOS nautical chart #13275. Contour interval is 2 m. See figure 4.4 for location of maps. Dashed lines show boundaries of physiographic zones, which are based on seafloor topography and dominant substrate properties. Bottom photographs A-C (middle) and seismic-reflection profile (bottom) are indicated by yellow circles and line, respectively. The distance across the bottom of the photographs is approximately 50 cm.