Federal Emergency Management Agency, Unknown, Floodplains: Federal Emergency Management Agency, Washington, DC.Online Links:
- www.fema.gov/msc
.
This is a Vector data set. It contains the following vector data types (SDTS terminology):
Planar coordinates are encoded using coordinate pair
Abscissae (x-coordinates) are specified to the nearest 0.061
Ordinates (y-coordinates) are specified to the nearest 0.061
Planar coordinates are specified in meters
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.
Sequential unique whole numbers that are automatically generated.
Coordinates defining the features.
Positive real numbers that are automatically generated.
Positive real numbers that are automatically generated.
1-800-358-9616 (voice)
www.fema.gov/msc
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.
The FIRM panels were scanned and the digital files were georeferenced using 1:24,000 USGS DRGs and DOQQs. The flood hazard zones were digitized from these FIRM panels. The FIRM panels were digitized at varying scales due to different map scales, resolution, and complexity. The following list contains the FIRM Community-Panel Number followed by the scale the FIRM was digitized at. 510218 0001--1:1200 510002 0001 C--1:1000 510001 0085 C--1:1200 510001 0105 C--1:400 510001 0150 C--1:1200 510001 0110 E--1:1200 510001 0075 C--1:400 510001 0040 C--1:400 510001 0035 C--1:1200 510001 0125 C--1,200 510001 0005 C--1:1200 510001 0120 C--1:1200 510001 0045 B--1:1200 510001 0050 D--1:1500 510001 0175 B--1:1200 510001 0095 C--1:1200 510001 0140 C--1:1200 510001 0090 D--1:1200 510001 0060 C--1:1200 510001 0135 C--1:1200 510001 0145 C--1:1200 510001 0160 C--1:1200 510001 0130 B--1:1200 510001 0115 B--1:400 510001 0025 B--1:1200 510001 0020 B--1:3000 510001 0180 C--1:1200 510001 0170 C--1:1200 510001 0065 B--1:1200 510001 0155 C--1:1200 510001 0100 C--1:1200 510001 0030 B--1:1200 510001 0080 C--1:2000 510001 0070 B--1:1200 510001 0165 B--1:1200 510003 0001 A--1:600 510005 0001 B--1:400 510242 0001 B--1:600 510218 0001 B--1:600 510298 0001 A--1:600
Data sources used in this process:
Federal Emergency Management Agency, Flood Insurance Rate Map, Accomack County, Virginia: Federal Emergency Management Agency, Washington, DC.
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.
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.
Vertical_Positional_Accuracy_Report: 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.
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.
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.
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 match 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.
1-800-358-9616 (voice)
www.fema.gov/msc
Downloadable Data
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.
| Data format: | ESRI Shapefile (version 1) |
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| Media you can order: |
CD-ROM
(format ISO 9660)
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| Data format: | MapInfo Interchange file (MIF) (version 1) |
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| Media you can order: |
CD-ROM
(format ISO 9660)
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| Data format: | ARCE (version 1) |
|---|---|
| Media you can order: |
CD-ROM
(format ISO 9660)
|
1-800-358-9616 (voice)
www.fema.gov/msc