Shoreline Data Rescue Project of Semidi Islands, ALlaska, CS319B

These data were automated to provide an accurate high-resolution historical shoreline of Semidi Islands, ALlaska suitable as a geographic information system (GIS) data layer. These data are derived from shoreline maps that were produced by the NOAA National Ocean Service including its predecessor agencies which were based on an office interpretation of imagery and/or field survey. The NGS attribution scheme 'Coastal Cartographic Object Attribute Source Table (C-COAST)' was developed to conform the attribution of various sources of shoreline data into one attribution catalog. C-COAST is not a recognized standard, but was influenced by the International Hydrographic Organization's S-57 Object-Attribute standard so the data would be more accurately translated into S-57. This resource is a member of https://www.fisheries.noaa.gov/inport/item/39808

The shoreline and associated data layers were originally intended to support NOAA Nautical Chart production. These datasets have been cleaned and reformatted to support the efforts of supplying accurate shoreline data layers for a coastal GIS database. These datasets may be beneficial for performing change analysis for erosion and accretion studies, land use planning, determination of boundary extent, and other types of decision making.

These shoreline data represent a vector conversion of a set of NOS raster shoreline manuscript identified by t-sheet or tp-sheet numbers. These vector data were created by contractors for NOS who vectorized georeferenced raster shoreline manuscripts using Environmental Systems Research Institute, Inc. (ESRI)(r), ArcInfo's(r) ArcScan(r) software to create individual ArcInfo coverages. The individual coverages were ultimately edgematched within a surveyed project area and appended together. The NOAA NESDIS Environmental Data Rescue Program (EDRP) funded this project. The NOAA National Ocean Service, Office for Coastal Management, developed the procedures used in this project and was responsible for project oversight. The project intent was to rescue valuable historical data and make it accessible and useful to the coastal mapping community. This process involved the conversion of original analog products to digital mapping products. This file is a further conversion of that product from a raster to a vector product that may be useful for Electronic Charting and Display Information Systems (ECDIS) and geographic information systems (GIS).

Information on shapefile attributes can be found at https://www.fisheries.noaa.gov/inport/item/60809

These data were generated for use by NGS during the course of its development of potential final products to fulfill its statutory mission. Although NGS is making these data available to others who may find the data of value, NGS does not warrant, endorse, or recommend the use of these data for any given purpose. The user assumes the entire risk related to the use of these data. These data are not for navigational purposes. NGS is providing these data "as is," and NGS disclaims any and all warranties, whether expressed or implied, including (without limitation) any implied warranties of merchantability or fitness for a particular purpose. In no event will NGS be liable to you or to any third party for any direct, indirect, incidental, consequential, special, or exemplary damages or lost profits resulting from any use or misuse of these data.

None

Data set is not for use in litigation. While efforts have been made to ensure that these data are accurate and reliable within the state of the art, NOAA, cannot assume liability for any damages, or misrepresentations, caused by any inaccuracies in the data, or as a result of the data to be used on a particular system. NOAA makes no warranty, expressed or implied, nor does the fact of distribution constitute such a warranty. We do request that you credit the National Oceanic and Atmospheric Administration (NOAA) when you use these data in a report, publication, or presentation.

Vector data was derived from

rectified raster images of NOS coastal survey maps using ArcInfo

processing software. These vector shoreline data are referenced to

the North American Datum of 1983. Vector shoreline extracted from

map images adequately represents the shoreline shown on original NOS

source surveys. The absolute value of the overall predicted horizontal

accuracy has not been determined. However, the

reports associated

with the project maps describe the process of producing the map source

and includes the horizontal control layout and if aerotriangulated,

the fit to control statistics. One may refer to the 6 March 1991

edition of 'Journal of Coastal Research' entitled 'Historical

Shoreline Change: Error Analysis and Mapping Accuracy' for an

independent accuracy assessment of vectorized NOS digital shoreline

conducted by the Federal Emergency Management Agency and the University

of Maryland.

All data are clipped to the neatline representing a surveyed project boundary. Line segments which did not close were snapped by the nodes to create consistently tied strings without node dangles.

The shoreline and associated data are a representation based on an office interpretation of imagery at the time of photographs taken 1941-01-01. To maintain shoreline continuity, a line with 'Shoreline/Alongshore Feature Boundary' attribution was added to the 'Shoreline' class. This feature is an artificial line that separates double-lined alongshore features from the shoreline. The 'Shoreline/Alongshore Feature Boundary' indicates to the user that a man-made alongshore feature is coincident to the shoreline in the data file. The rectangular geographic boundary limits is for data management purposes and does not infer complete surveyed coverage.

The shoreline and associated data are a representation based on an office interpretation of imagery and/or fieldwork at the time of survey. The attribute accuracy was tested by creating checkplots of the coded linework. The codes depict shoreline and several alongshore features. A light table review of the checkplots revealed any inaccurate coding. Mistakes were identified and corrected. These attributes were translated into NGS's Coastal Cartographic Object Attribute Source Table (C-COAST) for data consistency. The C-COAST attributes were given symbology and visually inspected to verify attribute accuracy.