THIS IS AN EXAMPLE OF HISTORIC T-SHEET METADATA AND SHOULD ONLY BE USED FOR FAMILIARIZATION WITH THE GENERAL PRODUCT. SEE INDIVIDUAL METADATA FOR EACH T-SHEET. The Coastal Section of the Mississippi Office of Geology is providing historic T-sheets for the Mississippi Coast in a georeferenced format for use with GIS systems. These maps are the earliest reliable indicators of shoreline position and shoreline type. They provide a wealth of information on the conditions that existed in the 1840'-1850's. They are useful for long-term shoreline change analysis and landcover change analysis. They are provided in Mississippi Transverse Mercator projection and were rectified using previously digitized shorelines from the maps. Shorelines were originally digitized by Louisiana State University through a contract with MOG in 1991. This data is usefull for a multitude of long-term studies looking at coastal change since the 1800's and for locating historical features such as structures and roads DO NOT USE FOR SPECIFIC T-SHEETS. Shoreline positions are also available as line features. The shorelines were digitized from the hard-copy mylar T-Sheets using coordinate conversions from the original datums and projections to UTM. If using in ArcMap 8x, in the image's Layer Properties, the Symbology tab, the 'Stretch Type' needs to be set to 'none' for best display quality. NOT FOR USE AS METADATA FOR INDIVIDUAL T-SHEETS. Should not be used for navigation or emergencies. Should not be used for legal purposes without significant analysis, and an understanding of the data. Attributes represent grey scale values from 0 to 255. The accuracy of the grey scale values was not checked, but the image quality (value) was adjusted for best viewing. Mylar T-sheets were scanned at 150 dpi and saved as .tif images in Corel PhotoPaint. The .tif images were imported into ArcMap and rectified using a previously digitized shoreline from each of the individual T-sheets. 10-20 reference points were selected for rectification. Points were spaced over the entire image, and were chosen based on recogonizable features. The image was rectified using an Afine transformation. The rectified .tif image was then converted to a .sid file using ArcTools. Reference points chosen to rectify the image were selected on the basis of matches between the scanned image and the digitized shoreline. Some errors in digitizing were noticed, these areas were not used. In some cases the mapped shoreline (image) was not clearly defined, the most likely linear feature matching the digitized shoreline was used. Since the digitized shoreline was originally completed from the map (image) it is only important that the two linear features match up. Accuracy is represented in meters. The difference between reference points on the digitized and image features was measured and a root mean square (rms) value determined. Two error values determine the actual ground error - digitizing error and georectifying error. Value represents rms error between digitized and image features in meters. Actual ground error will be higher. Actual ground error will be equal to digitized shoreline source error +/- the reported value above. A printout of control point errors is available as a txt file. Rms error of digitized shoreline base on values reported in: Historical Shoreline Change: Error Analysis and Mapping Accuracy, Crowell, Leatherman and Buckley, Journal of Coastal Research, v 7, n 3, pp 839-852, 1991. Source.

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Last Modified: April 23, 2016 @ 7:01 am