Older landslides in Tactic quadrangle, Guatemala

This cover contains the outlines of recent landslides formed prior to Hurricane Mitch in October - November 1998. Jeffrey Coe and Robert Bucknam mapped the landslides. Most landslides were mapped using 1:40,000-scale aerial photographs and a Kern PG-2 photogrammetric plotter at 4X and 8X magnifications. The photographs were scaled and oriented to the topographic base map using prominent topographic landmarks and plotted on a transparent polyester overlay registered to the topographic base maps at scales of 1:50,000 or 1:25,000. In areas where landslides were very sparse, the aerial photographs were scanned with a mirror stereoscope at 4X magnification, and landslide locations were transferred to base maps by inspection. The mapped landslides were digitized manually or by an optical scanner, and the data were then digitally registered to a digital version of the base map in ArcInfo.