AL1918-1957 - Vectorized Shoreline of Alabama Derived from 1918-1957 Source Data

There are critical needs for a nationwide compilation of reliable shoreline data. To meet these needs, the USGS has produced a comprehensive database of digital vector shorelines by compiling shoreline positions from pre-existing historical shoreline databases and by generating historical and modern shoreline data. Shorelines are compiled by state and generally correspond to one of four time periods: 1800s, 1920s-1930s, 1970s, and 1998-2002. Each shoreline may represent a compilation of data from one or more sources for one or more dates provided by one or more agencies. Details regarding source are provided in the 'Data Quality Information' section of this metadata report. Shoreline vectors derived from historic sources (first three time periods) represent the high water line at the time of the survey, whereas modern shorelines (final time period) represent the mean high water line.针对全国范围内可靠岸线数据的整合汇编存在迫切需求。为满足此类需求，美国地质调查局（USGS）通过整合现有历史岸线数据库中的岸线位置数据，并生成历史与现代岸线数据，构建了一套完整的数字矢量岸线数据库。岸线数据按州域进行汇编，且通常对应以下四个时间段之一：19世纪、1920年代至1930年代、1970年代以及1998年至2002年。每条岸线的数据可由一个或多个机构提供的、对应一个或多个观测日期的多源数据汇编而成。有关数据源的详细信息，请参阅本元数据报告的「数据质量信息」章节。源自历史数据源（前三个时间段）的岸线矢量数据代表测绘时的高潮线，而现代岸线（最后一个时间段）则代表平均高潮线。