Abstract:

This dataset contains information about the Base Flood Elevations (BFE) within a study area. BFE lines indicate the rounded whole-foot water surface elevation of the 1-percent-annual-chance flood. The spatial elements representing BFE features are lines extending from Special Flood Hazard Area (SFHA) boundary to SFHA boundary. The BFE lines will have no visible gaps or overshoots between the SFHA boundary and the end of the BFE line at the publication scale of the DFIRM. However, the ends of the BFE lines are not necessarily snapped precisely to the SFHA boundary. Each BFE is represented by a single line. The Base Flood Elevation (BFE) information is required for any digital data where BFE lines will be shown on the corresponding Flood Insurance Rate Map (FIRM). Normally if there are any riverine AE zones, BFE lines are required. While BFE lines are depicted as wavy lines on the hardcopy FIRM, they should be primarily straight lines in the spatial data, although they may bend consistent with procedures described in Volume 1 of these Guidelines. The Digital Flood Insurance Rate Map (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 (100 year), the 0.2-percent-annual-chance flood event (500 year), 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 FEMA. This dataset is an update to the DFIRM_BFE_MAY16 layer.

Purpose:

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 FIRM Database presents the flood risk 
information depicted on the FIRM in a digital format suitable for use in electronic 
mapping applications. The FIRM Database serves to archive the information 
collected during the Flood Risk Project.

Supplemental_Information:

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**The Following Information Contains The GeoPlan Center Process Steps: Indented Format** 
The GeoPlan Center downloaded the Statewide National Flood Hazard Layer 
from the following FEMA website on October 13th, 2017.

FEMA Flood Map Service Center
https://msc.fema.gov/portal
Search All Products
https://msc.fema.gov/portal/advanceSearch

Choose one of the three search options below and optionally enter a posting date range.
https://msc.fema.gov/portal/advanceSearch
State -FLORIDA
County - ALACHUA
Community - ALACHUA
 Search
 Effective Products
  NFHL Data-State(1)

Product ID Latest Study Effective Date Latest LOMR Effective Date Size Download
NFHL_12_20171006 10/05/2017 10/06/2017 1975MB

NFHL_12_20171006.zip
NFHL_12_20171006.gdb
  Feature Layer: S_BFE

The S_BFE was originally in the following projection:

GCS_North_American_1983
WKID: 4269 Authority: EPSG

Angular Unit: Degree (0.0174532925199433)
Prime Meridian: Greenwich (0.0)
Datum: D_North_American_1983
  Spheroid: GRS_1980
    Semimajor Axis: 6378137.0
    Semiminor Axis: 6356752.314140356
    Inverse Flattening: 298.257222101

The dataset was projected to the FGDL Albers HARN projection using the following Transformation:
NAD_1983_To_HARN_Florida

The dataset was renamed to dfirm_bfe_oct17.

Next the following fields were added and populated:
PRODUCT_ID = "NFHL_12_20171006"
DESCRIPT = [ELEV] and [LEN_UNIT] 
FGDLAQDATE = "10/13/2017"
AUTOID = OBJECTID

No methodology was performed by GeoPlan to correct for geometry issues.
For more information on FEMA's Final Data Structure concerning sliver polygons 
please see below.
The FEMA report frm_gsal.pdf states the following regarding sliver polygons.
L.3.5.2 Topology
Vector data files must meet the following data structure requirements:
* Area spatial features for a given theme must cover the entire study area 
without overlaps, underlaps or sliver polygons between adjacent polygons.

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** The following FEMA DFIRM information is from the frm_gsalb.pdf ** 
Table: S_BFE The Base Flood Elevation (BFE) table is required for any digital data 
where BFE lines will be shown on the corresponding Flood Insurance Rate Map 
(FIRM). Normally if there are any riverine AE zones, BFE lines are required. The 
S_BFE table contains information about the BFEs within a study area. A spatial file 
with locational information also corresponds with this data table. BFE lines indicate 
the rounded whole-foot water surface elevation of the 1-percent-annual-chance 
flood. The spatial elements representing BFE features are lines extending from 
Special Flood Hazard Area (SFHA) boundary to SFHA boundary. The BFE lines will 
have no visible gaps or overshoots between the SFHA boundary and the end of the
BFE line at the publication scale of the DFIRM. However, the ends of the BFE lines
are not necessarily snapped precisely to the SFHA boundary. Each BFE is 
represented by a single line. While BFE lines are depicted as wavy lines on the 
hardcopy FIRM, they should be primarily straight lines in the spatial data, although 
they may bend consistent with procedures described in Volume 1 of these 
Guidelines. 
Table: D_Length_Units LEN_LID LEN_UNIT 1000 CENTIMETERS 1010 FEET 
1020 INCHES 1030 KILOMETERS 1040 METERS 1050 MILES 
1060 MILLIMETERS
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FEMA Disclaimer: 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. The hardcopy FIRM and FIRM Database and the accompanying FIS 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. Acknowledgement of FEMA would be appreciated in products derived from these data.

The NFHL incorporates all FIRM Databases published by FEMA and any LOMRs that have been issued against those databases since their publication date. The NFHL consists of vector files and associated attributes produced in conjunction with the hardcopy FEMA FIRM. The published effective FIRM and FIRM Database 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 Standards for Flood Risk Analysis and Mapping. 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 the individual FIRM Database components of the NFHL 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 reports that accompany the individual FIRM Database components of the NFHL. Users should be aware that BFEs shown in the S_BFE table may 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.

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.

Data contained in the NFHL reflects 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. Generally, regulatory water surface elevations and/or regulatory floodways are published only for developed or developing areas of communities. For areas where little or no development is expected to occur, FEMA may generate flood risk data without published water surface elevations. Typically, only drainage areas that are greater than one square mile and with an average of one foot of flood depth or greater are studied. Note: The NFHL reflects the most current information available when the distribution data set was created. Currently, not all areas of a State or Territory have effective FIRM Database data. As a result, users may need to refer to the effective FIRM for effective flood hazard information.

The NFHL consists of vector files and associated attributes produced in conjunction with the hardcopy FEMA FIRM. The published effective FIRM and FIRM Database 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 Standards for Flood Risk Analysis and Mapping. The reliability of the floodplain boundary delineation is quantified by comparing the computed flood elevation to the ground elevation at the mapped floodplain boundary. The tolerance for how precisely the flood elevation and the ground elevation must match varies based on the flood risk class, which is a function of population, population density, and/or anticipated growth in floodplain areas. A horizontal accuracy of +/- 38 feet is used to determine the compliance with the vertical tolerances defined for each risk class. The range of differences between the ground elevation (defined from the topographic data used for the Flood Risk Project) and the computed flood elevation is between +/- 1.0 foot at the 95% confidence interval for areas with high population within the floodplain and/or high anticipated growth and Special Flood Hazard Areas (SFHAs) with high flood risk to +/- one-half the contour interval at the 85% confidence interval for areas with low population and densities within the floodplain and small or no anticipated growth and SFHAs with low flood risk. Independent quality control testing of the individual FIRM Database components of the NFHL was also performed.

The NFHL dataset is a compilation of effective FIRM Databases (a collection of the digital data that are used in GIS systems for creating new Flood Insurance Rate Maps) and Letters of Map Change (Letters of Map Amendment and Letters of Map Revision only) that create a seamless GIS data layer for a State or Territory. It is updated on a monthly basis. The FIRM Databases are compiled in conjunction with the hardcopy FIRMs and the final FIS reports. The specifics of the hydrologic and hydraulic analyses performed are detailed in the FIS reports available for each jurisdiction. The results of these studies are submitted in digital format to FEMA. These data and unrevised data from effective FIRMs are compiled onto the base map used for FIRM publication and checked for accuracy and compliance with FEMA standards. As new FIRM Databases are received the individual FIRM layers are sewn into the nationwide layers of the NFHL. LOMRs for the FIRM Databases in the NFHL are cut directly into the NFHL data layers as they are being produced and finalized.

The GeoPlan Center downloaded the Statewide National Flood Hazard Layer from the following FEMA website on October 13th, 2017. FEMA Flood Map Service Center https://msc.fema.gov/portal Search All Products https://msc.fema.gov/portal/advanceSearch Choose one of the three search options below and optionally enter a posting date range. https://msc.fema.gov/portal/advanceSearch State -FLORIDA County - ALACHUA Community - ALACHUA Search Effective Products NFHL Data-State(1) Product ID Latest Study Effective Date Latest LOMR Effective Date Size Download NFHL_12_20171006 10/05/2017 10/06/2017 1975MB NFHL_12_20171006.zip NFHL_12_20171006.gdb Feature Layer: S_BFE The S_BFE was originally in the following projection: GCS_North_American_1983 WKID: 4269 Authority: EPSG Angular Unit: Degree (0.0174532925199433) Prime Meridian: Greenwich (0.0) Datum: D_North_American_1983 Spheroid: GRS_1980 Semimajor Axis: 6378137.0 Semiminor Axis: 6356752.314140356 Inverse Flattening: 298.257222101 The dataset was projected to the FGDL Albers HARN projection using the following Transformation: NAD_1983_To_HARN_Florida The dataset was renamed to dfirm_bfe_oct17. Next the following fields were added and populated: PRODUCT_ID = "NFHL_12_20171006" DESCRIPT = [ELEV] and [LEN_UNIT] FGDLAQDATE = "10/13/2017" AUTOID = OBJECTID No methodology was performed by GeoPlan to correct for geometry issues. For more information on FEMA's Final Data Structure concerning sliver polygons please see below. The FEMA report frm_gsal.pdf states the following regarding sliver polygons. L.3.5.2 Topology Vector data files must meet the following data structure requirements: * Area spatial features for a given theme must cover the entire study area without overlaps, underlaps or sliver polygons between adjacent polygons.

Flood Risk Project Identifier. For a single-jurisdiction flood risk project, the value is composed of the 2-digit state FIPS code and the 4-digit FEMA CID code (e.g., 480001). For a countywide flood risk project, the value is composed of the 2-digit state FIPS code, the 3-digit county FIPS code, and the letter C (e.g., 48107C). Within each FIRM database, the DFIRM_ID value is identical.

Length Units. This unit indicates the measurement system used for the BFEs and/or depths. Normally this would be feet. This field is only populated if the STATIC_BFE or DEPTH field is populated. Acceptable values for this field are listed in the D_Length_Units table.

Vertical Datum. The vertical datum indicates the reference surface from which the flood elevations are measured. Normally this would be North American Vertical Datum of 1988 for new studies. This field is only populated if the STATIC_BFE field is populated. Acceptable values for this field are listed in the D_V_Datum table.

Source Citation. Abbreviation used in the metadata file when describing the source information for the S_Fld_Haz_Ar table. Normally, the flood hazard area polygon will be divided to distinguish areas modified by the most recent revision from areas based on the effective FIRM prior to the most recent revision. Revisions and sources prior to the most recent revision will not be tracked for individual polygons in the flood hazard areas table in the standard database.

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. Table containing attribute information associated with the data set. FEMA FIRM Database Technical Reference (available in the FEMA Library at http://www.fema.gov/media-library/assets/documents/34519).

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. The following tables are included in this data set: l_comm_info l_stn_start study_info s_bfe s_base_index s_firm_pan s_fld_haz_ar s_fld_haz_ln s_gen_struct s_label_ld s_perm_bmk s_pol_ar s_pol_ln s_quad_index s_wtr_ln s_xs s_label_pt

The Florida Geographic Data Library is a collection of Geospatial Data compiled by the University of Florida GeoPlan Center with support from the Florida Department of Transportation. GIS data available in FGDL is collected from various state, federal, and other agencies (data sources) who are data stewards, producers, or publishers. The data available in FGDL may not be the most current version of the data offered by the data source. University of Florida GeoPlan Center makes no guarantees about the currentness of the data and suggests that data users check with the data source to see if more recent versions of the data exist. Furthermore, the GIS data available in the FGDL are provided 'as is'. The University of Florida GeoPlan Center makes no warranties, guaranties or representations as to the truth, accuracy or completeness of the data provided by the data sources. The University of Florida GeoPlan Center makes no representations or warranties about the quality or suitability of the materials, either expressly or implied, including but not limited to any implied warranties of merchantability, fitness for a particular purpose, or non-infringement. The University of Florida GeoPlan Center shall not be liable for any damages suffered as a result of using, modifying, contributing or distributing the materials. A note about data scale: Scale is an important factor in data usage. Certain scale datasets are not suitable for some project, analysis, or modeling purposes. Please be sure you are using the best available data. 1:24000 scale datasets are recommended for projects that are at the county level. 1:24000 data should NOT be used for high accuracy base mapping such as property parcel boundaries. 1:100000 scale datasets are recommended for projects that are at the multi-county or regional level. 1:125000 scale datasets are recommended for projects that are at the regional or state level or larger. Vector datasets with no defined scale or accuracy should be considered suspect. Make sure you are familiar with your data before using it for projects or analysis. Every effort has been made to supply the user with data documentation. For additional information, see the References section and the Data Source Contact section of this documentation. For more information regarding scale and accuracy, see our webpage at: http://geoplan.ufl.edu/education.html

BASE FLOOD ELEVATION (BFE) LINES OF THE DIGITAL FLOOD INSURANCE RATE MAP (DFIRM) IN THE STATE OF FLORIDA - OCTOBER 2017

Metadata: