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<br />\;b\liJding to t~e predicte~,~~~~~l~y~~on level is diffic~lt. It is,tleverthe\~\ incumbent on
<br />/;,~~mmumty, d~Ve:l:!rJler;er'property owner to estabhshaBFE for plann4l~ purposes or
<br />.</ forp'pJposes SJI-tequesting a map amendment or revision. \ \
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<br />/'<>,/ \'\ ,\._,/,>,/ /<-=_=>__. .... \ _ _.___~!,:,~~E::"--" -- _ __~
<br />/ /. Accura'ey.of Hydrologic antl;ll~ta~TIJe relative accuracy of flQQd.level;::::-/-\
<br />/;:> predictio~~i>ased onth>~bility ofhist;)ncQata~tlie:m_e;tl:mtillo.g1ii:appned,~d the \,
<br />// level of detAff~vail'!-\:lllCt6 create a mathematical modeL T~~ relative accuracy ol}hese \ \, ZONE
<br />calculations vartes:atso by the nature of the terrain being stj1~ied and the type ofpooding. />\\ X
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<br />""', The ny'1luffactors,that affect map accuracy, the various in,~"rpretations of"accurac'y'~"v/ r", '\ \
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<br />\;" and the,~(aj complexity'of~ood mapping indicate the need fori ~ thorough study of accuracy
<br />\~\ iss~~l1ich the Council ex;Je~s to undertake. ' '
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<br />/::// 4.2 Digital Mapping-:>>\
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<br />Most of the 80,gOO::Plus NFIP ~ap,panels were prepared between the mid-1970s and the
<br />mid-1980s, when tl)..ll'J~~sive conversion 6t\(?mmunities from the Emergency to the Regular
<br />Program occurr;d;,(see ':4.1(I:endix IL "Evolut'kzn of Maps" for discussion). These maps were
<br />prepared usjng:manual sciilli!1g techniques that't~olved the negative engraving of the
<br />informatiC1~{o be shown on .It!:!", NFIP map onto scti~ecoat. Scribecoat is a material consisting of
<br />a plastic b~ covered with an '~que emulsion. T~~artographer engraves the necessary
<br />informatiori\~o the scribecoat, ~tQ.oving the opaque'c.(\,:,ering and leaving a negative imprint of
<br />the scribed infQh(lation. Different't~es ofinformation)sl.!~h as roads, floodplains, and labels,
<br />are scribed onto 's~arate sheets of scFi~ecoat and t~er(.over.lll,id. After overlaying these sheets, a
<br />positive im~ge coih~i~g the informailQf,on thejetlarate s~ets, or ':layers," is prepared for .
<br />photographic reprod~,on of the final mllp~~1~ls layered appr~ch IS advantageous because It
<br />allows for revising infOiJI\ation OlLonej:liyei;' such as the floodp~h boundaries, without altering
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<br />or modifying the informati~lier layers, such as roads or polit~al boundaries. At the time
<br />these maps were produced, scribing was state-of-the-art in cartography" As computer technology
<br />has evolved, however, digital mapping techniques have emerged and at~'g~nerally much !ll,Sler-:::,::::;::
<br />and easier than manual scribing. /:~:~:~;~;::"=:~:::::::::""
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<br />FEMA recognizes the nee~t9_cmlY~t~inaP~mgifal:fu;.fuiIt-an(j~~b to do so in the
<br />late 1980s, pro<!1tcing-dtgjraJ::f{RM-S1J)FlRMs)'using- digital base maps prepaf~bY local or state
<br />Z~L,,_,:::~~r~t::~~rl~aerai-agencT~s. During the first few ~ears o~producti?n'~aIe DFIRMs
<br />"c:c:::::=:::::::::'w~e'prod'uced usmg V.S, Census Bureau TIGER data but thiS practIce was dlscontli1\~d due to
<br />-- " the limited quality of the data. The conversion to digital maps is constrained by fiscaloill;llities.
<br />As a greater proportion of the NFIP mapping budget is expended on reviewing letters of~p
<br />correction (LOMCs), the FEMA budget for map study and restudy has declined, meaning't4at the
<br />number of map panels being revised or updated is relatively small compared to the total num~~
<br />of panels in the NFIP inventory. '<\
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<br />When a map revision or update affects only a small percentage of a community's total ,
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<br />NFIP map panels, it is considered to be cost-prohibitive to convert the maps to digital format. In
<br />these cases, manually scribed materials are revised. Sometimes, the panels affected by the update
<br />ZONEX
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