This online map application assesses current and future flood hazards for the City of Boston for floods driven by coastal storms. The interactive map displays the extent of the current 10-year, 100-year, and 500-year floods. It uses the "bathtub mapping" assumption to show how water from the harbor would spread horizontally over land, using the requirement that pathways through which the water flows must be connected so that water cannot go through a high berm.

Sea level rise can increase the likelihood of these coastal flooding events significantly. An attached document provides the future return periods (or annual percent chances) of the floods for median and high-end sea level rise scenarios in the 2020s, 2050s, and 2080s. For example, with the median estimate of sea level rise by 2055 of 36 cm (just over one foot), the flood area and depth that has a current return period of 100 years will have a return period in 2055 of 53.6 years.

The map enables the user to explore infrastructure that will be flooded by each flood level. The infrastructure includes transportation networks and stops; government, residential, commercial, and industrial buildings; schools; hospitals; pharmacies; grocery stores; historical landmarks; and green spaces.