| Content Citation |
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Title of Content: |
USGS 15 and 30 minute Historical Maps for San Francisco Bay Area
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Type of Content: |
raster digital data |
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Content Publisher: |
U. S. Geological Survey |
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Publication Place: |
Menlo Park, CA |
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Publication Date: |
October, 2004 |
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| Content Description |
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Content Summary:
Both the 15-minute and 30-minute USGS quadrangle series have been abandoned. These historical maps are merely images and are not georeferenced for direct use in a GIS.
Original topographic maps in our archives were scanned as full size images (generally 18 x 22 inches). Images were scanned at 400 dpi in 24 bit RGB color in a .tiff file format then compressed in MeSID format. Filenames are a combination of the map name, the edition date, and the reprint date, if noted below the edition date.
For selected images, photo-processing has been completed to enhance the image. Processing was performed using Adobe Photoshop software and may include the following procedures;
Erasure of graffiti - extraneous hand written marks in the map margin have been removed.
Color correction - color values have been adjusted to remove the effects of aging of the paper.
Image Brightness - image contrast has been enhanced.
One can calculate an approximate pixel size from the scale of the map (1:62500 or 1:125000). The original projection for the maps was Polyconic (projection parameters are unknown). The ellipsoid would have been Clarke 1866. The datum at the bottom of the map is mean sea level.
GIS software is required to georeference the information and fit control points to a data set with a known projection system. If you have ESRI ArcGIS software, the following web page is useful (http://www.gsd.harvard.edu/gis/manual/georeferencing/index.htm). Also see the ESRI ArcGIS help on georeferencing a raster data set. Other help sources are available if you search using the terms, "georeferencing images". |
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Content Purpose:
Historical maps have been used to estimate geospatial changes particularly in urban areas. Changes in bay wetlands, rivers, and coastlines have also been inferred from historical maps. For USGS studies see the USGS Urban Dynamics site (http://landcover.usgs.gov/urban/intro.php). |
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| Time Period of Content |
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Beginning Date: |
1899 |
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Ending Date: |
1961 |
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| Content Status |
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Progress: |
Complete |
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Update Frequency: |
None Planned |
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| Content Keywords |
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Theme Keywords: |
topographic map, printed map, USGS 15 minute quadrangle map, USGS 30 minute quadrangle map |
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Place Keywords: |
California, San Francisco Bay and Delta, Alameda County, Sonoma County, Napa County, Marin County, Contra Costa County, San Francisco County, San Mateo County, Santa Clara County, Solano County |
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| Spatial Data Information |
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Data Type: |
raster digital data
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Data Format: |
MrSID compressed format |
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| Access and Usage Information |
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Access Constraints: |
None. |
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Use Constraints: |
None. Acknowledgement of the U.S. Geological Survey would be appreciated in products derived from these data. |
