Floodplains Outline from 2020

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, the 0.2-percent-annual-chance flood event, 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 the Federal Emergency Management Agency (FEMA). The file is georeferenced to earth's surface using the UTM projection and coordinate system. The specifications for the horizontal control of DFIRM data files are consistent with those required for mapping at a scale of 1:12000. 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 DFIRM Database presents the flood risk information depicted on the FIRM in a digital format suitable for use in electronic mapping applications. The DFIRM database is a subset of the Digital FIS database that serves to archive the information collected during the FIS.数字洪水保险费率地图（Digital Flood Insurance Rate Map, DFIRM）数据库用于呈现洪水风险信息，以及用于生成该风险数据的配套支撑数据。该数据库采用的核心风险分级包括：年超越概率1%的洪水事件、年超越概率0.2%的洪水事件，以及最低洪水风险区域。DFIRM数据库的数据源自洪水保险研究（Flood Insurance Studies, FISs）、此前发布的洪水保险费率地图（Flood Insurance Rate Maps, FIRMs）、为支撑FISs与FIRMs开展的洪水灾害分析，以及可用的新型测绘数据。上述FISs与FIRMs均由联邦紧急事务管理局（Federal Emergency Management Agency, FEMA）发布。该数据集采用通用横轴墨卡托（Universal Transverse Mercator, UTM）投影与坐标系完成地球表面地理配准。DFIRM数据文件的水平控制规范与1:12000比例尺测绘的要求保持一致。其保险应用场景包括落实《洪水灾害保护法案》的强制投保要求：该法案要求，在获取或改造位于已识别特殊洪水危险区内或计划设于该区域内的土地设施时，接受联邦项目援助，或由联邦监管、监督或保险的机构或单位提供协助的房产所有者，必须购买洪水保险，相关条款出自1973年《洪水灾害保护法案》第2(b)(4)节。除识别特殊洪水危险区（Special Flood Hazard Areas, SFHAs）外，FIRMs上标注的风险分区亦是通过全国洪水保险计划（National Flood Insurance Program, NFIP）提供的洪水保险保费费率制定的核心依据。DFIRM数据库将FIRMs上展示的洪水风险信息转换为适用于电子测绘应用的数字格式。DFIRM数据库是数字FIS数据库的子集，用于归档FIS开展过程中收集的相关信息。