NORCAL1854_1880 - Vectorized Shoreline of Northern California from 1854-1880 Source Data

There are critical needs for a nationwide compilation of reliable shoreline data. To meet these needs, the U.S. Geological Survey (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.构建全国范围内可靠岸线数据集的需求十分迫切。为满足此类需求，美国地质调查局（U.S. Geological Survey, USGS）通过整合现有历史岸线数据库中的岸线位置数据，并自主生成历史与现代岸线数据，构建了一套覆盖全面的数字矢量岸线数据库。岸线数据按州进行整合，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。每条岸线可能整合了单个或多个机构提供的、对应单个或多个观测日期的多源数据。有关数据来源的详细说明，请参见本元数据报告的"Data Quality Information"章节。源自历史数据源的岸线矢量（即前三个时间段的岸线）代表测绘时的高水位线，而现代岸线（即最后一个时间段的岸线）则代表平均高水位线。