REQUIRED: The name of an organization or individual that developed the data set., REQUIRED: The date when the data set is published or otherwise made available for release., SDETrims.DBO.Hydro_FloodFEMAQ3.Online Links:
- Service=sde:sqlserver:CHUCKNORRIS; Database=SDETrims; Version=dbo.DEFAULT
This is a Vector data set. It contains the following vector data types (SDTS terminology):
Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.000000. Longitudes are given to the nearest 0.000000. Latitude and longitude values are specified in Decimal degrees.
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.
Coordinates defining the features.
Sequential unique whole numbers that are automatically generated.
Coordinates defining the features.
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 puchase 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 1973 Flood Disaster Protection Act). In addition to the identification of Special Flood Hazard Areas, the risk zones shown on the FIRMs are the basis for the establishment of premium rates for flood coverage offered through the NFIP. Q3 Flood Data files are intended to convey certain key features from the existing hard copy FIRM to provide users with automated flood risk data. Edge-matching errors, overlaps and deficiencies in coverage, and similar problems are not corrected during digitizing or post-processing. These data may be used to locate Special Flood Hazard Areas (SFHAs). More detailed information may be obtained from the paper FIRM.
Data sources used in this process:
The Q3 Flood Data are countywide vector files derived from the FEMA Flood Insurance Rate Maps (FIRMS). The attribute definitions may be found in the "Q3 Flood Data Specfications". Attribute accuracy was tested by manual comparison of source graphic with hardcopy plots and a symbolizied display on an interactive computer graphic system. Selected attributes that could not be visually verified were individually queried. In addition, an ARC/INFO Arc Macro Language (AML) software program was applied to the dataset to test the attributes against a master set of valid attributes for the specific data category, and a complete set of valid attribute combinations. (See also Entity Attribute Information).
Specifications for the digitizing of FIRMs to create the Q3 Flood Data are consistent with those requirements for mapping at a scale of 1:24000. Horizontal control of Q3 Flood Data was established using USGS quadrangle maps at 1:24000 or other standard scales. Users should assess the horizontal positional sources and the requirements of their application. With increased frequency, large-scale spatial data sets are becoming widely available for computer-based geographic information systems. Q3 Flood Data may be used in combination with other digital spatial data, however, users should be aware that scalar enlargements do not enhance the relative accuracy of the Q3 Flood Data (i.e. 1:24000).
Data completeness for Q3 Flood Data files reflect the content of the source graphic. Features may have been eliminated or generalized on the source graphic, due to scale and legibility constraints. 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 analysis 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 anaylses are used to generate flood risk data only for developed or developing areas of communities. For undeveloped 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. The Q3 Flood Data coverages may be derived from DFIRM-DLGs, from FIRM- DLGs, from FIRMs digitized previously for emergency applications, or may be newly created files. In Q3 Flood Data derived from older data sets, certain items may not have been captured or may have been captured differently from the current Q3 Flood Data specifications. In some cases, preliminary FIRM data have been included in the Q3 Flood Data files. These data have been provided to the community for their review and comment and may be subject to change before their final publication date. In addition, in some cases areas designated as Flood Prone Areas on maps prepared by USGS and FIA have been included in the Q3 Flood Data files. These areas were delineated based on available information on past floods and are described by a unique attribute code that distinquishes them from areas of 1% annual chance of flooding derived from FIRMs. Flood Insurance Rate Maps continually undergo revisions and updates. Some of these revisions are effected by letter (Letter of Map Revision (LOMR), Letter of Map Amendment (LOMA)). Q3 Flood Data may not reflect the most current information or information that is not mappable at the publication scale of FIRM. To obtain the latest information, contact the address listed under distributor.
Polygon and chain-node topology are present. Certain node-area-line relationships are collected or generated to satisfy topological requirements. Some of these requirements include: lines must begin and end at nodes, lines must connect to each other at nodes, lines do not extend through nodes, left and right areas are defined for each line segment and are consistent throughout the files, and the lines representing the limits of the file neatlines are free of gaps. Tests of logical consistency were performed by ARC/INFO software modules. Check plots were made to test for leaks in all internal polygons.
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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.
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