def dump_csv(output)
      csv = CSV.new(output)
      csv << ["GEOID", "Name", "CBSA", "Population", "Housing Units", "Land Area", "Water Area"]
      metropolitan_division_data.each do |geoid, data|
        csv << [geoid, data[:name], data[:cbsa], data[:population], data[:housing_units], data[:land_area]&.round(3), data[:water_area]&.round(3)]