TERMDEFINITION
The fundamental type of flow treated in open-channel hydraulics. The depth of flow and velocity does not change in either magnitude or direction with respect to time at any point or cross section.
    1-percent annual chance floodplain:
This is the boundary of the flood that has a 1-percent chance of being equalled or exceeded in any given year. Also known as the 100-year floodplain.
    1-percent annual chance stillwater elevation:
The projected elevation of the flood having a 1% chance of being equalled or exceeded in any given year (100-year flood), in the absence of waves resulting from wind or seismic effects, referenced to the National Geodetic Vertical Datum, North American Vertical Datum, or other datum.
    1-percent annual chance water-surface elevation:
The height, in relation to the National Geodetic Vertical Datum of 1929 (or other datum, where specified), of the flood having a 1-percent chance of being equaled or exceeded in any given flood year (also known as the 100-year flood or the base flood).
    10-percent annual chance stillwater elevation:
The projected elevation of the flood having a 10% chance of being equalled or exceeded in any given year, in the absence of waves resulting from wind or seismic effects, referenced to the National Geodetic Vertical Datum, North American Vertical Datum, or other datum.
    100-year flood:
The flood having a 1-percent chance of being equalled or exceeded in any given year; also known as the base flood. The 1-percent annual chance flood, which is the standard used by most Federal and state agencies, is used by the National Flood Insurance Program (NFIP) as the standard for floodplain management and to determine the need for flood insurance. A structure located within a special flood hazard area shown on an NFIP map has a 26 percent chance of suffering flood damage during the term of a 30-year mortgage.
    100-year floodplain:
This is the boundary of the flood that has a 1-percent chance of being equalled or exceeded in any given year. Officially termed the 1-percent annual chance floodplain.
    500-year floodplain:
This is the boundary of the flood that has a 0.2-percent chance of being equalled or exceeded in any given year. Officially termed the 0.2-percent annual chance floodplain.
This WHAFIS input card represents an area where the ground elevation temporarily rises above the 1% annual chance stillwater elevation, such as a high dune or other land mass. The stillwater elevation on the inland side may differ from that on the seaward side, though the station elevation on either side of the AS line segment must equal the applicable stillwater elevation on that side.
    Accuracy:
This term refers to the conformance to a reasonable standard. The statistical meaning of accuracy is the degree with which an estimated mean differs from the true mean. Different projects require different levels of data accuracy than others. The National Standard for Spatial Data Accuracy (NSSDA) has implemented a well-defined statistic and testing methodology for the positional accuracy of maps and geospatial data derived from sources such as aerial photographs, satellite imagery, or maps. Accuracy specifications for data collection during a FEMA Flood Insurance Study are outlined in several FEMA-authored guidance documents.
    Alluvial Fan Flooding:
Flooding occurring on the surface of an alluvial fan or similar landform which originates at the apex and is characterized by high velocity flows; active processes of erosion, sediment transport, and deposition; and unpredictable flow paths.
    Approach Slope:
The 1 on 40 sloping portion of the retreated dune profile, which lies immediately seaward of the 1 on 1 sloping dune face.
    Area Data:
A fundamental unit of geographic information; it is a measure of a particular extent of the earth`s surface.
    Attribute:
A characteristic of a geographic feature described by numbers, characters, images and CAD drawings, typically stored in tabular format and linked to the feature by a user-assigned identifier (e.g., the attributes of a well might include depth and gallons per minute). Also used to refer to a column in a database table that describes or quantifies characteristics of the special data.
    Automated Floodplain Mapping:
The use of digital elevation models (DEMs) or digital terrain models with digital water surface elevation data in the GIS environment to define the limits of the floodplain.
The effect of downstream flow on the water-surface profile.
    Backwater Effect:
The effect of downstream flow on the water-surface profile.
    Base Flood:
The flood having a 1-percent chance of being equaled or exceeded in any given year; also known as the 100-year flood. The base flood, which is the standard used by most Federal and state agencies, is used by the National Flood Insurance Program (NFIP) as the standard for floodplain management and to determine the need for flood insurance. A structure located within a special flood hazard area shown on an NFIP map has a 26 percent chance of suffering flood damage during the term of a 30-year mortgage.
    Base Flood Elevation (BFE):
The height of the base flood, usually in feet, in relation to the National Geodetic Vertical Datum of 1929, the North American Vertical Datum of 1988, or other datum referenced in the Flood Insurance Study report, or depth of the base flood, usually in feet, above the ground surface.
    Base map:
A map containing geographic features (e.g., roads) used for locational reference.
    Basement:
The bottom floor (basement or underground garage) is below ground level (grade) on all sides. Structures constructed above crawl spaces that are below grade on all sides are classified as an enclosure.
    Bathymetric Map:
A map depicting elevations of the earth`s surface at or below 0.0 NGVD (or other datum), that is, below the overlying water column.
    Block Group (data):
A geographic area bounded on all sides by visible or nonvisible features shown on census maps. A block group is the third smallest geographic entity for which the Census Bureau collects and tabulates decennial census information.
    Buffer:
A zone of a specified distance around spatial features. Both constant-width and variable-width buffers can be generated for a set of spatial features based on each feature's attribute values. The resulting buffer zones form polygons that are either inside or outside the specified buffer distance from each feature. Buffers are useful for proximity analysis (e.g., find all stream segments within 300 feet of a proposed logging area.)
    Buildings (BU):
This WHAFIS input card represents an area where buildings (or groups of buildings) dissipate wave energy.
A hydraulics application designed to quickly and accurately verify the validity of an assortment of parameters in the HEC-2 program.
    Channel Bank Stations:
Points that identify the extreme limits of the natural stream channel. These stations are typically assigned at locations along a cross section where a relatively flat area exists outside of the channel.
    Coastal Hazard Analysis Modeling Program (CHAMP):
CHAMP is a Windows-interfaced Visual Basic program that allows the user to enter data, perform coastal engineering analyses, view and tabulate results, and chart summary information for each representative transect along a coastline within a user-friendly graphical interface.
    Coastal High Hazard Area (CHHA):
An area of special flood hazard extending from offshore to the inland limit of a primary frontal dune along an open coast and any other area subject to high velocity wave action from storms or seismic sources. CHHAs are indicated as V or VE Zones on the Flood Insurance Rate Maps.
    Community Map Repository:
The location where a community`s flood maps are kept; usually the local zoning and planning office.
    Computer-aided design (CAD):
A computer-based system for the design, drafting, and display of graphically oriented information.
    Conditional Letter of Map Amendment (CLOMA):
FEMA`s formal comment on whether a proposed structure(s) would be excluded from the Special Flood Hazard Area shown on the effective NFIP map. This letter does not revise or amend an effective NFIP map.
    Conditional Letter of Map Revision (CLOMR):
A letter from FEMA commenting on whether a proposed project, if built as proposed, would meet the minimum standards of the National Flood Insurance Program.
    Confluence:
A location where two streams or rivers meet.
    Contour:
A line on a map joining points of equal altitude.
    Coordinate system:
A reference system used to measure horizontal and vertical distances on a planimetric map. A coordinate system is usually defined by a map projection, a spheroid of reference, a datum, one or more standard parallels, a central meridian, and possible shifts in the x- and y-directions to locate x,y positions of point, line, and area features. A common coordinate system is used to spatially register geographic data for the same area.
    Coordinates:
Any of a set of numbers that determines the location of a point in a space of a given dimension.
    Crawlspace:
The bottom floor is below the first floor, is enclosed by solid or partial perimeter walls, and is above ground level (grade) on at least one side.
    Critical Depth:
The depth of flow at which, for a given discharge at a given location, the total energy is the minimum value possible for flow to occur.
    Cross Section:
A line developed from topographic information across a floodplain at which a computation of flood flow has been made to establish a potential flood elevation. Cross sections are shown on the Flood Boundary Floodway Map, Flood Insurance Rate Map, and/or Flood Profiles of a Flood Insurance Study.
A collection of related records.
    Datum:
A fixed starting point of a scale.
    Density:
The number of inhabitants per unit in a geographic region.
    Deposit Area:
The area of the upper shoreface that receives the approximately 540 square feet of sand eroded from the retreated frontal dune or bluff, characterized by a landward 1 on 40 slope and a seaward 1 on 12.5 slope.
    Depth:
Maximum depth of water in the cross section as measured below the water-surface elevation.
    Digital Flood Insurance Rate Map (DFIRM):
As part of FEMA`s Map Modernization Objectives, a new Digital Flood Insurance Rate Map (DFIRM) product is being developed. The new DFIRM product will include a spatial database with options that can be invoked depending on the available data. The DFIRM spatial database will include certain standard features and meet minimum mapping requirements. Additional enhancements will be included depending on community needs, available data, and funding. A review of needs and available data will lead to recommendations concerning which options to exercise.
    Digital Orthophoto Quadrangle (DOQ):
Base map data supplied by communities or other non-Federal sources (e.g., State or regional agencies) that meet FEMA criteria will be the first choice for new DFIRM production. Digital Orthophoto Quarter Quadrangles (DOQs) produced by the U.S. Geological Survey (USGS) will be the second choice and the default base map if suitable community data are not available. If neither suitable community base map data nor USGS DOQs are available for a county scheduled for new DFIRM production, FEMA will provide the community with information on base map sources, including information on partnering with USGS to initiate DOQ production for that county.
    Digital Terrain Model:
A computer representation of the altitude of the earth`s surface, which consists of spot elevations at regularly spaced intervals in the horizontal direction in the form of a grid.
    Digitizing:
The process of converting map data from their original visual form (i.e., a paper map) to digital format that can be handled by a computer.
    Discharge:
The volume of water that passes a given location within a given period of time. Usually expressed in cubic feet per second (cfs).
    Discrete (cells):
Self-contained, distinct units.
    Drawdown:
The water-surface profile will lower in the upstream direction if the water-surface elevation (WSEL) at the upstream cross section is lower than the WSEL at the downstream cross section. This is called a drawdown. The Federal Emergency Management Agency does not allow a drawdown to be shown on flood profiles. To eliminate a drawdown, the upstream WSEL should be made graphically equal to the downstream WSEL. The computed values in the computer model output should not be changed to eliminate drawdowns.
    Drawing File Format (DWG):
Default file format for vector graphics used by many Computer-Aided Design and Drafting systems.
    Drawing Interchange Format (DXF):
A commonly used ASCII or binary file format used for the exchange of graphic data. This format is widely used as the de facto format for transferring drawings between Computer-Aided Design and Drafting systems.
    Dune:
Under the National Flood Insurance Program, natural or artificial ridges or mounds of sand located landward of the beach.
    Dune (DU):
This WHAFIS input card represents an area where wave energy is dissipated across a flooded sand dune or other natural or manmade, elongated barrier (e.g., levee, seawall).
    Dune Reservoir:
The cross sectional area of the frontal dune that lies above the 1% annual chance stillwater elevation and seaward of the dune peak (in a ridge-type dune) or rear shoulder (in a mound-type dune).
Height of the land surface relative to NGVD or other vertical datum.
    End Transect (ET):
This WHAFIS card is used to identify the last station in the transect, and is required.
    Energy Grade:
Depth of water plus velocity head - V2/2G.
    Erosion:
Under the National Flood Insurance Program, the process of the gradual wearing away of land masses. In general, erosion involves detachment and movement of soil and rock fragments, either over the course of hours or days during a flood or storm, or over a period of years through the action of wind, water, or other geologic processes.
    Erosion Assessment:
To account for storm-induced erosion, an Erosion Assessment was established as part of the standard FEMA coastal methodology in 1989. If the cross-sectional area lying above the 1% annual chance stillwater elevation and seaward of the peak of the Primary Frontal Dune is less than 540 square feet, the dune is considered completely eroded during a base flood event. If the area is greater than or equal to 540 square feet, the dune retreats. Each resulting condition has an associated post-storm geometry, which is described in detail in the modeling section of this tutorial.
The eroded face of the retreating frontal dune or bluff, characterized by 1 on 1 slope extending seaward from the dune peak. The 540 square feet of eroded material is taken from above the 1% annual chance stillwater elevation and seaward of this slope.
    Federal Emergency Management Agency (FEMA):
An independent agency of the Federal government, founded in 1979, which reports directly to the President. FEMA is responsible for identifying and mitigating natural and man-made hazards. The agency`s mission is:

To reduce loss of life and property and protect our nation`s critical infrastructure from all types of hazards through a comprehensive, risk-based, emergency management program of mitigation, preparedness, response, and recovery.
    Fetch:
The distance over which wind acts on the water surface to generate waves.
    Fill:
Any earthen material used to raise the ground to or above the Base Flood Elevation (BFE).
    Flood (also Flooding):
A general and temporary condition of partial or complete inundation of normally dry land areas. For flood insurance claim purposes, two or more structures must be inundated before flood damage will be covered.
    Flood Boundary Floodway Map (FBFM):
A pre-Map Initiatives floodplain management map that delineates the 100-year (1% annual chance) and 500-year (0.2% annual chance) floodplains, floodway, and cross sections.
    Flood Hazard Boundary Map (FHBM):
Initial map issued by FEMA to identify approximate Special Flood Hazard Areas (SFHA`s) within a community.
    Flood Hydrograph:
A graph showing water discharge after a flood.
    Flood Insurance Rate Map (FIRM):
A map on which the 100-year (1% annual chance) and 500-year (0.2% annual chance) floodplains, Base Flood Elevations, and risk premium zones (and floodway information on Map Initiatives FIRMs) are delineated to enable insurance agents to issue accurate flood insurance policies to homeowners in communities participating in the National Flood Insurance Program.
    Flood Insurance Study (FIS):
An examination, evaluation, and determination of flood hazards and, if appropriate, corresponding water-surface elevations. The resulting reports are used to develop Flood Insurance Rate Maps. Also known as a flood elevation study.
    Flood Map Production Coordination Contractor (FMPCC):
Coordinates projects and provides technical support to FEMA. Duties of the FMPCC include: Researching available data for scoping activities; Completing base map research and providing independent quality assurance and control of study contractor and Cooperating Technical Community products; DFIRM production; Preliminary and post-preliminary processing; and Evaluation of National Flood Insurance Program Regulations, Part 65 revision and Part 70 amendment requests.
    Flood Profile:
A cross-sectional drawing showing the contiguous cross sections along a stream, with ground elevations and potential flood elevations plotted.
    Flood hazard data:
Information about a community`s flooding hazards used to prepare Flood Insurance Rate Maps and Flood Insurance Study reports. It may include information such as statistical analyses of records of river-flow, storm tides, and rainfall; information obtained through consultation with the community; floodplain topographic surveys; and hydrologic and hydraulic analyses.
    Floodplain Management:
The operation of a program of corrective and preventative measures for mitigating flood damage, including, but not limited to, emergency preparedness plans, flood-control works, and floodplain management regulations.
    Floodplain or Flood-Prone Area:
Any land area susceptible to inundation by water from any source.
    Floodway:
Channel of a stream plus any adjacent floodplain areas that must be kept free of encroachment so that the 100-year flood discharge can be conveyed without increasing the elevation of the 100-year flood by more than a specified amount (1 foot in most states).
    Flow Regimes:
The combined effects of viscosity, channel slope, cross-sectional geometry and flow magnitude create a range of flow regimes in open channels. There are three different flow regimes (subcritical, supercritical, and mixed flow) where the relation between depth of flow and specific energy varies.
    Frequency Analysis (also Flood Frequency Analysis):
Statistical techniques that estimate the probabilities of a flood event occurring.
Assigning locational coordinates, such as longitude/latitude, to map features (i.e., assigning a point location on the earth for a mailing address.)
    Geographic Information System (GIS):
A Geographic Information System (GIS) is a computer-based system used to capture, store, analyze and display geographic information.
    Georeferenced:
An image referenced to another image using geographic coordinates.
    Geospatial:
Spatial data with geographic coordinates associated with it.
    Global Positioning System (GPS):
The Global Positioning System (GPS) is a satellite-based radio navigation system developed and operated by the U.S. Department of Defense (DOD). It allows land, sea, and airborne users to determine their three-dimensional position, velocity and time precisely and accurately, 24 hours a day, in all weather, anywhere in the world. Each GPS satellite transmits an accurate position and time signal. GPS receivers collect signals from the satellites and display the user`s position, velocity, and time as needed for their marine, terrestrial, or aeronautical applications.
PC-based GIS software used to implement a standardized, nationally applicable earthquake loss estimation method. The Hazus software is being expanded to perform similar loss evaluations for wind (hurricanes, thunderstorms, tornadoes, extra tropical cyclones and hail) and flood (riverine and coastal) hazards. Hazus development is being funded by FEMA through a cooperative agreement with the National Institute of Building Sciences.
    HEC-1:
A computer program developed by the US Army Corps of Engineers Hydrologic Engineering Center for use in simulating the surface runoff response of a river basin to precipitation.
    HEC-2:
A step-backwater program developed by the US Army Corps of Engineers Hydrologic Engineering Center for use in calculating water-surface profiles for steady, gradually varied flow in natural or man-made channels.
    Housing Unit (data):
A house, an apartment or other group of rooms, or a single room, is regarded as a housing unit when it is occupied or intended for occupancy (not live and eat with any other persons in the structure) and if there is direct access from the outside or through a common hall.
    Hurricane:
A tropical cyclone formed in the atmosphere over warm ocean areas, in which wind speeds equal or exceed 74 miles per hour and blow in a large spiral around a relatively calm center or `eye.` Hurricane circulation is counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
    Hydraulic Engineering Center-River Analysis System (HEC-RAS):
A step-backwater program developed by the US Army Corps of Engineers Hydrologic Engineering Center for use in calculating water surface profiles for both steady and unsteady gradually varied flow. The system can handle a full network of channels, a dendritic system, or a single river reach. The software is available for download from the HEC Web site at http://www.hec.usace.army.mil/software/hec-ras.
    Hydraulic Radius:
Equal to (Area of cross section / Wetted Perimeter).
InterFerometric Synthetic Aperture Radar. It uses airborne or space-borne radar antennae to obtain highly accurate terrain data over larger geographic areas.
    Ineffective flow areas:
An area of a cross section that will contain water that is not actively being conveyed. These areas are often used to describe portions of a cross section in which water will pond, but the velocity of that water, in the downstream direction, is close to zero.
    Initial Elevation (IE):
This WHAFIS input card describes the initial overwater fetch, wave conditions, and stillwater elevation for the first segment of the transect, starting at elevation 0.0 NGVD (or other datum). This line segment is required.
    Inland Fetch (IF):
This WHAFIS input card represents an area where waves are regenerated across somewhat sheltered fetches and over shallow inland water bodies, using a sustained wind speed of 60 miles per hour.
    Interpolated:
A value calculated from values at neighboring stations.
Light Detection And Ranging. Airborne laser system that combines a pulsing laser with a positioning system consisting of a Global Positioning System (GPS) receiver and an Inertial Measuring Unit (IMU) to measure the elevation of ground points on the earth`s surface.
    Labeling:
Identifying a spatial feature with a descriptive word, phrase or number (e.g., placing the road name next to the line representing the road).
    Layer:
A thematic set of spatial data described and stored in a database or map library. Layers organize a database or map library by subject matter (e.g., soils, roads, and wells).
    Letter of Map Amendment (LOMA):
Official amendment, by FEMA, of a community`s effective National Flood Insurance Program map to remove structure(s) or lot(s) from the floodplain that have not been elevated above the base flood elevation by placement of fill.
    Letter of Map Revision (LOMR):
A letter from FEMA officially revising the current NFIP map to show changes to floodplains, floodways, or flood elevations.
    Letter of Map Revision Based on Fill (LOMR-F):
Official amendment, by FEMA, of a community`s effective National Flood Insurance Program map to remove structure(s) or lot(s) from the floodplain when they have elevated above the Base Flood Elevation by the placement of fill.
    Levee:
A man-made structure, usually an earthen embankment, designed to contain, control, or divert the flow of water in order to provide flood protection.
    Line Data:
One of the basic geographical primitives. It is defined by at least two pairs of XY coordinates.
    Lowest Adjacent Grade:
The lowest ground touching the structure.
Coefficient used to account for the friction caused by earthen, vegetative, and/or man-made surfaces within a floodplain cross section. The coefficient, n, is commonly used to represent flow resistance for hydraulic computations of flow in open channels. The procedure for selecting n values is subjective and requires judgment and skill that is developed primarily through experience. The expertise necessary for proper selection of n values can be obtained in part by examining characteristics of channels that have known or verified roughness coefficients. A table of Mannings values is available from the pull-down menu in the Quick-2 program.
    Manual Cartographic Methods:
Manual cartography uses a system of compiling artwork layers to produce a composite image of a map. Cartographers prepare each artwork layer by hand, using methods that are required for each layer, such as scribing, opaquing, and typesetting. Each artwork piece depicts certain map features that will only be shown on that layer of artwork. The layers are merged (through a photographic process that requires each artwork piece to be exposed on a piece of film) to produce a composite map image.
    Map Initiatives:
A Flood Insurance Rate Map format developed in 1985 that incorporates information formerly shown on the separately printed Flood Boundary Floodway Map (FBFM) (e.g., floodways and cross sections). Also referred to as combined Flood Insurance Rate Map/FBFM.
    Map Modernization Plan:
Plan developed by FEMA in 1997 to modernize its flood mapping program. The Plan`s goal is to upgrade the flood map inventory by:Developing up-to-date flood hazard data for all floodprone areas nationwide to support sound floodplain management and prudent flood insurance decisions; Providing the maps and data in digital format to improve the efficiency and precision with which mapping program customers can use this information; Fully integrating FEMA`s community and state partners into the mapping process to build on local knowledge and efforts; Improving processes to make it faster to create and update the maps; Improving customer services to make the maps easier to get and raise public awareness of flood hazard.
    Map Service Center (MSC):
The Map Service Center (MSC) distributes National Flood Insurance Program (NFIP) products including: Digital Flood Insurance Rate Maps (DFIRM), Flood Insurance Rate Maps (FIRM), Flood Insurance Studies (FIS), Digital Q3 flood data, Community Status Book, Flood Map Status Information Service (FMSIS), and Letters of Map Change (LOMC).
    Map compilation:
The collection and standardization of flood map data to produce DFIRMs.
    Map projection:
A mathematical model that transforms the locations of features on the Earth`s surface to locations on a two-dimensional surface. Because the Earth is three-dimensional, some method must be used to depict a map in two dimensions. Some projections preserve shape; others preserve accuracy of area, distance, or direction. Map projections project the Earth`s surface onto a flat plane. However, any such representation distorts some parameter of the Earth`s surface be it distance, area, shape, or direction.
    Marsh Grass (MG):
When a VH card is used in WHAFIS to represent an area characterized by marsh grasses, additional data concerning the size and density of each vegetation type must be provided through the MG option in the VH dialog box.
    Metadata:
"Data about data" describe the content, quality, condition, and other characteristics of data. Other characteristics may include the history of the data (who created it, how it was processed), contact information and accuracy information (e.g., error in points that were located with a GPS).
Federal insurance program under which flood-prone areas are identified and flood insurance is made available to residents of participating communities that agree to adopt and enforce floodplain management ordinances to reduce future flood damage.
    Normal Depth:
The depth expected for a stream when the flow is uniform, steady, one-dimensional, and is not affected by downstream obstructions or flow changes. This is the usual calculation that is utilized to determine Base Flood Elevations for property or structures in approximate (Zone A) areas.
    Northeaster:
An extra-tropical cyclonic weather system characterized by long duration, long fetch, and large area of circulation, occurring in late fall to early spring.
The area of a cross section that is found outside of the channel bank stations on either side of the stream channel.
    Overwater Fetch (OF):
This WHAFIS input card represents an area characterized by an unobstructed fetch over large bodies of water (water depth greater than 10 feet), where wave energy is regenerated using a sustained wind speed of 80 miles per hour.
In ridge-type dunes, the seawardmost topographic high reached before the land surface slopes back down toward the dune heel; the dune peak used for the Erosion Assessment is this seaward peak, which may not necessarily be the absolute highest elevation reached in any landward area of the dune or dune field. In mound-type dunes, where there is relatively little elevation change between two or more undulations in the dune surface, the dune peak is considered the rear shoulder, or landwardmost high point before the land surface drops off rapidly to the dune heel.
    Peak Discharge:
The peak volume of water that passes a given location within a given period of time. Usually expressed in cubic feet per second.
    Perpendicular to Flow Path:
Cross sections should be plotted so that they are oriented in a manner that is perpendicular to the flow path. Plotting cross sections in this manner requires that the user examine the topography to determine the direction in which the water is most likely to flow in relation to different points along the proposed cross section line. Typically, this can be achieved by ensuring that the cross section line crosses each contour on the topographic map at or near a 90 degree angle.
    Physical Map Revision (PMR):
A reprinted NFIP map incorporating changes to floodplains, floodways, or flood elevations. Because of the time and cost involved to change, reprint, and redistribute an NFIP map, a PMR is usually processed when a revision reflects large scope changes.
    Planimeter:
An instrument used to measure the area of a watershed by tracing its boundary line on a topographic map.
    Point Data:
A position, place, or locality.
    Polygon:
A multi-sided figure representing an area on a map; a geographic primitive.
    Primary Frontal Dune:
Under the National Flood Insurance Program, a continuous or nearly continuous mound or ridge of sand with relatively steep seaward and landward slopes immediately landward and adjacent to the beach and subject to erosion and overtopping from high tides and waves during major coastal storms. The inland limit of the primary frontal dune occurs at the point where there is a distinct change from a relatively steep slope to a relatively mild slope.
    Projection:
A system of intersecting lines, as the grid of a map, on which part or all of the globe or the celestial sphere may be shown as a plane surface.
A digital representation of certain features of FEMA`s Flood Insurance Rate Map (FIRM) product, intended for use with desktop mapping and GIS technology. Because of the scale of the digital Q3 Flood Data, it cannot be used to determine absolute delineations of flood risk boundaries.