U.S. Geological Survey Open-File Report 79–1314
Landslides and Related Features, Pennsylvania [Pittsburgh
1- by 2-Degree Sheet]
General Notes on Imaging
The maps presented on this site were scanned from film (positive) copies of the original maps. The copies were provided many years ago by the U.S. Geological Survey, the publisher of this report. The quality of the copies varies, but it is generally fair to poor, largely due to the reproduction methods available at that time for hard-copy compilations. On many of the films, the topographic and cultural base map is not visible or only faintly visible over wide areas, and the background is dark, containing numerous streaks and spots. Many of the original maps were spliced together within the map area, and these splice lines are noticeable on the copies as darker horizontal bands. In short, the images generally reflect the quality of the film positives.
The maps were scanned in monochrome mode at 400 dpi in order to drop as much of the dark background as possible and to produce smaller file sizes. They were saved in uncompressed TIFF format. Using raster editing software, the upper neatline of each map was rotated to horizontal, the images were digitally cleaned somewhat in the marginal and explanation areas, and sheets were cropped to a uniform size. PDF files were made from the edited images.