National Flood Hazard - Cross Sections

Normally, any FIRM that has associated flood profiles has cross sections. The S_XS table contains information about cross section lines. These lines usually represent the locations of channel surveys performed for input into the hydraulic model used to calculate flood elevations. Sometimes cross sections are interpolated between surveyed cross sections using high accuracy elevation data. Depending on the zone designation (Zone AE, Zone A, etc.), these locations may be shown on Flood Profiles in the FIS report and can be used to cross reference the Flood Profiles to the planimetric depiction of the flood hazards. This information is used in the Floodway Data Tables in the FIS report, as well as on the FIRM panels.<div><p style='margin-top: 0px; margin-bottom: 1.55rem; font-family: &quot;Avenir Next W01&quot;, &quot;Avenir Next W00&quot;, &quot;Avenir Next&quot;, Avenir, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; font-size: 17px;'>Flood hazard and supporting data are developed using specifications for horizontal control consistent with 1:12,000–scale mapping. If you plan to display maps from the National Flood Hazard Layer with other map data for official purposes, ensure that the other information meets FEMA’s standards for map accuracy.</p><p style='margin-top: 0px; margin-bottom: 1.55rem; font-family: &quot;Avenir Next W01&quot;, &quot;Avenir Next W00&quot;, &quot;Avenir Next&quot;, Avenir, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; font-size: 17px;'>The minimum horizontal positional accuracy for base map hydrographic and transportation features used with the NFHL is the NSSDA radial accuracy of 38 feet. USGS imagery and map services that meet this standard can be found by visiting the Knowledge Sharing Site (KSS) for <a href='http://pm.riskmapcds.com/kss/Lists/KSS_Standards2/DispForm.aspx?ID=2566' style='color: rgb(0, 121, 193); text-decoration: none;'>Base Map Standards (420)</a>. Other base map standards can be found at<a href='https://riskmapportal.msc.fema.gov/kss/MapChanges/default.aspx' style='color: rgb(0, 121, 193); text-decoration: none;'>https://riskmapportal.msc.fema.gov/kss/MapChanges/default.aspx</a>. You will need a username and password to access this information.</p><p style='margin-top: 0px; margin-bottom: 1.55rem; font-family: &quot;Avenir Next W01&quot;, &quot;Avenir Next W00&quot;, &quot;Avenir Next&quot;, Avenir, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; font-size: 17px;'>The NFHL data are from FEMA’s Flood Insurance Rate Map (FIRM) databases. New data are added continually. The NFHL also contains map changes to FIRM data made by Letters of Map Revision (LOMRs).</p><p style='margin-top: 0px; margin-bottom: 1.55rem; font-family: &quot;Avenir Next W01&quot;, &quot;Avenir Next W00&quot;, &quot;Avenir Next&quot;, Avenir, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; font-size: 17px;'>The NFHL is stored in North American Datum of 1983, Geodetic Reference System 80 coordinate system, though many of the NFHL GIS web services support the Web Mercator Sphere projection commonly used in web mapping applications. </p></div>

Tags: cross-sections, dfirm, fema, flood, nfhl, open-data
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