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Open-File Report 97–470 A: Data Processing Steps
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Data processing steps are briefly described as follows:

1. Geological boundaries were traced on mylar from original paper map sheets. Then mylars were used to produce binary scanned images on a large format Anatech Eagle scanner. A separate image was created for each of the five paper sheets.

2. Binary imagesof geologic boundaries from step 1 were converted to vector files with the ARC/INFO GRIDLINE utility and then supplemented by manual digitization.

3. Geologic age attributes were assigned to the ArcInfo polygon coverages from step 2.

4. ArcInfo coverages from step 3 were transformed to Transverse Mercator projection with the central meridian equal to 160 E and a scale factor at central meridian equal to 0.945.

5. Original paper map sheets were also scanned on the Anatech Eagle scanner in gray-scale mode. There were two images of every map sheet - binary (after mylar scanning) and gray - scale (after original map scanning). Both images were in TIFF format at 200 dot/inch resolution.

6. Gray scale images from step 5 were georeferenced with ArcInfo REGISTER and RECTIFY utilities. ArcInfo coverages from step 4 were used as reference. No rubber transformations were involved.

7. Polygon boundaries and geologic attributing of the ARC/INFO coverages from step 4 were verified and corrected by using gray - scale images from step 6 as a background images.

8. Final ArcInfo coverages (geology, geologic provinces, oil and gas centerpoints) were projected to Geographic coordinates with the ArcInfo PROJECT utility.

9. ArcGIS 8.1 dataset "Personal Database" was created by importing coverages from step 8.

10. ArcMap 8.1 project was created from data in step 9. Mercator projection with central meridian at 250 E was set up as display projection.

11. The plot files in Adobe .PDF format ( /win/plot directory) were compiled entirely in ESRI's ArcMAP 8.1 environment.

Administrative and country boundary coverages used on the map are the property of Environmental Systems Research Institute, Inc. (ESRI) and are used with permission.

Data is provided both unprojected (geographic coordinates) and projected coordinates.
Projection - Mercator, False Easting: 0.0, False Northing: 0.0
Central Meridian: 25.0
Standard Parallel: 0.0

Description of Map Units
Keys to Provinces

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U.S. Geological Survey Open File Report  97- 470A, ver. 2.0