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Digital Flood Insurance Map (DFIRM) Database for Connecticut - Base Flood Elevation Lines (BFE)

Frequently-asked questions:


What does this data set describe?

Title:
Digital Flood Insurance Map (DFIRM) Database for Connecticut - Base Flood Elevation Lines (BFE)

Abstract:
Includes location and attributes for Base Flood Elevation Lines (BFE) shown on Digital Flood Insurance Rate (DFIRM) maps available for five Connecticut counties. See below for time period of each county DFIRM Database included in this statewide BFE layer. More current data may be available from the Federal Emergcy Management Agency (FEMA). The DFIRM Database depicts flood risk information and supporting data used to develop the risk data. The primary risk classifications used are the 1-percent-annual-chance flood event, the 0.2-percent-annual-chance flood event, and areas of minimal flood risk. The DFIRM Database is derived from Flood Insurance Studies (FISs), previously published Flood Insurance Rate Maps (FIRMs), flood hazard analyses performed in support of the FISs and FIRMs, and new mapping data, where available. The FISs and FIRMs are published by the Federal Emergency Management Agency (FEMA). The file is georeferenced to earth's surface using the State Plane projection and coordinate system. The specifications for the horizontal control of DFIRM data files are consistent with those required for mapping at a scale of 1:12,000.

Supplemental information:
In Guidelines and Specifications for Flood Hazard Mapping Partners (http://www.fema.gov/library/viewRecord.do?id=2206), FEMA defines technical requirements, product specifications for Flood Hazard Maps and related National Flood Insurance Program (NFIP) products, and associated coordination and documentation activities. 



  1. How should this data set be cited?

    Federal Emergency Management Agency, varies, Digital Flood Insurance Map (DFIRM) Database for Connecticut - Base Flood Elevation Lines (BFE): Federal Emergency Management Agency, Washington, DC.

    Online links:
  2. What geographic area does the data set cover?

    Bounding coordinates:
    West: -73.689110
    East: -71.784053
    North: 42.036804
    South: 41.005058

  3. What does it look like?

    http://www.cteco.uconn.edu/metadata/fema/browsegraphic/fema_dfirmfullview.gif (GIF)
    Full view of DFIRM for Connecticut with data available for Fairfield, Hartford, Middlesex, New London, and New Haven counties.

    http://www.cteco.uconn.edu/metadata/fema/browsegraphic/fema_dfirmdetailview.jpg (JPEG)
    Detail view of DFIRM Database with standard FEMA symbology

    http://www.cteco.uconn.edu/metadata/fema/browsegraphic/fema_dfirmcolorsymbologydetailview.jpg (JPEG)
    Detail view of DFIRM Database with color symbology applied by CT DEEP

    http://www.cteco.uconn.edu/metadata/fema/browsegraphic/fema_firm_legend.gif (GIF)
    Legend for FEMA Flood Insurance Rate Maps (FIRM)

    http://www.cteco.uconn.edu/metadata/fema/browsegraphic/fema_firm_notes_to_users.gif (GIF)
    Notes to users included on FEMA Flood Insurance Rate Maps (FIRM)

  4. Does the data set describe conditions during a particular time period?

    Calendar date: 20100618
    Calendar date: 20110916
    Calendar date: 20080828
    Calendar date: 20110718
    Calendar date: 20101217
    Currentness reference:
    FIRM and FIS effective date for Fairfield, Hartford, Middlesex, New London, and New Haven Counties, respectively.

  5. What is the general form of this data set?

    Geospatial data presentation form: FEMA-DFIRM-Final

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      Indirect spatial reference:
      { Describe location of data in terms of attributes included in the data that denote geographic location. For example: Connecticut Town name and number; Connecticut stream name and number; Basin name and number; Zip code. }

      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • String (18635)

    2. What coordinate system is used to represent geographic features?

      The map projection used is Lambert Conformal Conic.

      Projection parameters:
      Lambert Conformal Conic
      Standard parallel: 41.200000
      Standard parallel: 41.866667
      Longitude of central meridian: -72.750000
      Latitude of projection origin: 40.833333
      False easting: 999999.999996
      False northing: 499999.999998

      Planar coordinates are encoded using coordinate pair.
      Abscissae (x-coordinates) are specified to the nearest 0.000328.
      Ordinates (y-coordinates) are specified to the nearest 0.000328.
      Planar coordinates are specified in survey feet.

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.

      Vertical coordinate system definition:
      Altitude system definition:
      Altitude resolution: 1.000000
      Altitude encoding method: Explicit elevation coordinate included with horizontal coordinates

  7. How does the data set describe geographic features?

    BFE
    Base Flood Elevation Lines. See http://www.cteco.uconn.edu/metadata/fema/document/frm_selected_pages_from_Appendix_L.pdf for attribute definitions. (Source: Federal Emergency Management Agency)

    OBJECTID
    Internal feature number. (Source: ESRI)
                      

    Sequential unique whole numbers that are automatically generated.

    BFE_LN_ID
    ELEV
    LEN_UNIT
    V_DATUM
    SOURCE_CIT
    Shape
    Feature geometry. (Source: ESRI)
                      

    Coordinates defining the features.

    Shape.len
    Entity and attribute overview:
    The DFIRM Database is made up of several data themes containing both spatial and attribute information. These data together represent the current flood risk for the subject area as identified by FEMA. The attribute tables include SFHA locations, flood zone designations, BFEs, political entities, cross-section locations, FIRM panel information, and other data related to the NFIP.
    

    Entity and attribute detail citation:
    Appendix L of FEMA's Guidelines and Specifications for FEMA Flood Hazard Mapping Partners contains a detailed description of each attribute code and a reference to other relevant information.
    
    Entity and attribute detail citation:
    The following tables are included in this data set: l_comm_info l_mt1_lomc l_stn_start study_info s_bfe s_cbrs s_base_index s_firm_pan s_fld_haz_ar s_fld_haz_ln s_gen_struct s_label_pt s_label_ld s_perm_bmk s_pol_ar s_pol_ln s_quad_index s_wtr_ln s_xs
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Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)


  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    Federal Emergency Management Agency
    500 C Street, S.W.
    Washington , District of Columbia 20472
    USA

    1-800-358-9616 (voice)
    http://www.fema.gov/msc
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Why was the data set created?

The FIRM is the basis for floodplain management, mitigation, and insurance activities for the National Flood Insurance Program (NFIP). Insurance applications include enforcement of the mandatory purchase requirement of the Flood Disaster Protection Act, which "... requires the purchase of flood insurance by property owners who are being assisted by Federal programs or by Federally supervised, regulated or insured agencies or institutions in the acquisition or improvement of land facilities located or to be located in identified areas having special flood hazards," Section 2 (b) (4) of the Flood Disaster Protection Act of 1973. In addition to the identification of Special Flood Hazard Areas (SFHAs), the risk zones shown on the FIRMs are the basis for the establishment of premium rates for flood coverage offered through the NFIP. The DFIRM Database presents the flood risk information depicted on the FIRM in a digital format suitable for use in electronic mapping applications. The DFIRM database is a subset of the Digital FIS database that serves to archive the information collected during the FIS.

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How was the data set created?

  1. Where did the data come from?

    County DFIRM (source 1 of 2)

    Federal Emergency Management Agency, Connecticut County DFIRM Database: Federal Emergency Management Agency, Washington, DC.

    Online links:
    Other citation details:
    DFIRM Database publiciation dates vary according to county

    Type of source media: disc

    Connecticut DFIRM (source 2 of 2)

    Connecticut statewide DFIRM Database.

    Type of source media: disc

  2. What changes have been made?

    Date: 20110901 (change 1 of 1)
    Appended and added together available county-level DFIRM data to create a statewide feature class for Connecticut for use by the Connecticut Department of Energy and Environmental Protection.

    Person responsible for change:
    Courtney Larson
    Connecticut Department of Energy and Environmental Protection
    79 Elm Street
    Hartford, Connecticut 06106
    USA

    860-424-3540 (voice)

    Data sources used in this process:
    • County DFIRM

    Data sources produced in this process:
    • Connecticut DFIRM

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How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

    The DFIRM Database consists of countywide vector files and associated attributes produced in conjunction with the hard copy FEMA FIRM. The published effective FIRM and DFIRM maps are issued as the official designation of the SFHAs. As such they are adopted by local communities and form the basis for administration of the NFIP. For these purposes they are authoritative. Provisions exist in the regulations for public review, appeals and corrections of the flood risk information shown to better match real world conditions. As with any engineering analysis of this type, variation from the estimated flood heights and floodplain boundaries is possible. Details of FEMA's requirements for the FISs and flood mapping process that produces these data are available in the Guidelines and Specifications for Flood Hazard Mapping Partners.  Attribute accuracy was tested by manual comparison of source graphics with hardcopy plots and a symbolized display on an interactive computer graphic system. Independent quality control testing of FEMA's DFIRM database was also performed. To obtain more detailed information in areas where Base Flood Elevations (BFEs) and/or floodways have been determined, users are encouraged to consult the Flood Profiles and Floodway Data and/or Summary of Stillwater Elevations tables contained within the FIS report that accompanies this DFIRM database. Users should be aware that BFEs shown in the S_BFE table represent rounded whole-foot elevations. These BFEs are intended for flood insurance rating purposes only and should not be used as the sole source of flood elevation information.  Accordingly, flood elevation data presented in the FIS report must be used in conjunction with the FIRM for purposes of construction and/or floodplain management.  The 1-percent-annual-chance water-surface elevations shown in the S_XS table match the regulatory elevations shown in the FIS report.

  2. How accurate are the geographic locations?

    The DFIRM Database consists of countywide vector files and associated attributes produced in conjunction with the hardcopy FEMA FIRM. The published effective FIRM and DFIRM are issued as the official designation of the SFHAs. As such they are adopted by local communities and form the basis for administration of the NFIP. For these purposes they are authoritative. Provisions exist in the regulations for public review, appeals and corrections of the flood risk information shown to better match real world conditions. As with any engineering analysis of this type, variation from the estimated flood heights and floodplain boundaries is possible. Details of FEMA's requirements for the FISs and flood mapping process that produces these data are available in the Guidelines and Specifications for Flood Hazard Mapping Partners.  Horizontal accuracy was tested by manual comparison of source graphics with hardcopy plots and a symbolized display on an interactive computer graphic system. Independent quality control testing of FEMA's DFIRM database was also performed.
    

  3. How accurate are the heights or depths?

    The DFIRM Database consists of countywide vector files and associated attributes produced in conjunction with the hardcopy FEMA FIRM. The published effective FIRM and DFIRM maps are issued as the official designation of the SFHAs. As such they are adopted by local communities and form the basis for administration of the NFIP. For these purposes they are authoritative. Provisions exist in the regulations for public review, appeals and corrections of the flood risk information shown to better match real world conditions. As with any engineering analysis of this type, variation from the estimated flood heights and floodplain boundaries is possible. Details of FEMA's requirements for the FISs and flood mapping process that produces these data are available in the Guidelines and Specifications for Flood Hazard Mapping Partners.  Vertical accuracy was tested by manual comparison of source graphics with hardcopy plots and a symbolized display on an interactive computer graphic system. Independent quality control testing of FEMA's DFIRM database was also performed

  4. Where are the gaps in the data? What is missing?

    Data contained in the DFIRM Database files reflect the content of the source materials.  Features may have been eliminated or generalized on the source graphic, due to scale and legibility constraints.  With new mapping, FEMA plans to maintain full detail in the spatial data it produces.  However, older information is often transferred from existing maps where some generalization has taken place. Flood risk data are developed for communities participating in the NFIP for use in insurance rating and for floodplain management. Flood hazard areas are determined using statistical analyses of records of river flow, storm tides, and rainfall; information obtained through consultation with the communities; floodplain topographic surveys; and hydrological and hydraulic analysis. Both detailed and approximate analyses are employed. Generally, detailed analyses are used to generate flood risk data only for developed or developing areas of communities. For areas where little or no development is expected to occur, FEMA uses approximate analyses to generate flood risk data. Typically, only drainage areas that are greater than one square mile are studied.
    

  5. How consistent are the relationships among the observations, including topology?

    When FEMA revises an FIS, adjacent studies are checked to ensure agreement between flood elevations at the boundaries.  Likewise flood elevations at the confluence of streams studied independently are checked to ensure agreement at the confluence.  The FIRM and the FIS are developed together and care is taken to ensure that the elevations and other features shown on the flood profiles in the FIS agree with the information shown on the FIRM.  However, the elevations as shown on the FIRM are rounded whole-foot elevations.  They must be shown so that a profile recreated from the elevations on the FIRM will match the FIS profiles within one half of one foot.
    

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How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access constraints: None.
Use constraints:
The hardcopy FIRM and DFIRM and the accompanying FISs are the official designation of SFHAs and Base Flood Elevations (BFEs) for the NFIP.  For the purposes of the NFIP, changes to the flood risk information published by FEMA may only be performed by FEMA and through the mechanisms established in the NFIP regulations (44 CFR Parts 59-78). These digital data are produced in conjunction with the hardcopy FIRMs and generally matches the hardcopy map exactly.  However the hardcopy flood maps and flood profiles are the authoritative documents for the NFIP. Acknowledgement of FEMA would be appreciated in products derived from these data.

Distributor 1 of 1

  1. Who distributes the data set?

    FEMA, Map Service Center
    P.O. Box 1038
    Jessup, Maryland 20794-1038
    USA

    1-800-358-9616 (voice)
    http://www.fema.gov/msc
    Contact Instructions:
    Data requests must include the full name of the community or county and the FIRM panel number(s) or the 7.5- minute series quadrangle sheet area(s) covered by the request.
    

  2. What's the catalog number I need to order this data set?

    DFIRM_S_BFE

  3. What legal disclaimers am I supposed to read?

    No warranty expressed or implied is made by FEMA regarding the utility of the data on any other system nor shall the act of distribution constitute any such warranty. FEMA will warrant the delivery of this product in a computer-readable format, and will offer appropriate adjustment of credit when the product is determined unreadable by correctly adjusted computer input peripherals, or when the physical medium is delivered in damaged condition. Requests for adjustment of credit must be made within 90 days from the date of this shipment from the ordering site.

  4. How can I download or order the data?

  5. Is there some other way to get the data?

  6. What hardware or software do I need in order to use the data set?

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Who wrote the metadata?

Dates:
Last modified: 20111227

Metadata author:
MipHelp (subsequently modified by Howie Sternberg, CT DEEP, to describe the Connecticut DFIRM data based on the county-level DFIRM database)
Federal Emergency Management Agency
500 C Street, s.w
Washington , District of Columbi 1-877-336-2627
USA

1-877-336-2627 (voice)
miphelp@riskmapcds.com
Hours of Service: Monday to Friday, 08:30 to 16:30 Eastern Standard Time

Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata(FGDC-STD-001-1998)

Metadata extensions used:
  • http://hazards.fema.gov
  • http://www.epsg.org
  • http://www.esri.com/metadata/esriprof80.html

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