One map showing where Boston thinks FEMA erred: Gray is for flood areas the city agrees with, blue areas the city thinks don't deserve the designation and red the areas the city thinks should be added.

Even as they are appealing roughly a third of the 1,500 acres the federal government wants to add to maps of areas likely to flood in a "100-year" event, Boston officials are acknowledging that, ultimately, property owners of large sections of land along the coast and city rivers will have to face the costs of flood insurance because of rising sea levels.