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<br />1'l OG1L: 3 <br /> <br />prevailing or "acceptable" risk is probably higher, for example, in an alpine <br />ski resort where snow avalanches, landslides, etc., are commonplace and total <br />control is impossible and infeasible. <br /> <br />MAPPING 11! COLORADO <br /> <br />Selection of Map Scale and Format <br /> <br />Map scale and format should be determined by the level of detail necessary to <br />depict the particular problem area, the land use being considered, and data <br />being presented. However, other factors such as limited funds, manpower, or <br />time may actually have more control over the final product. The USGS (1982) <br />notes that all landslide hazard maps "...are a compromise between detail and <br />reliability and the difficulty and cost of preparation." <br /> <br />The choice of map scale is frequently designed to take advantage of standard <br />topographic base maps and aerial photographs. Creating maps at scales <br />different from existing mapping requires the meticulous transferal of <br />topographic and geologic information from other maps. In addition to <br />consuming a great deal of time and money, this process may introduce serious <br />errors. <br /> <br />One of the most useful mapping techniques for planners and public officials is <br />the superimposition of landslides on orthophotographic base maps or aerial <br />photographs. The ability to identify actual land or man-made features <br />heightens the awareness of the landslide hazard. <br /> <br />Base Maps <br /> <br />A base map is necessary before most investigations involving either <br />environmental geology, or land-use planning can be undertaken. Topographic <br />maps are the best base maps for most purposes. They show contours, or lines <br />connecting all points of equal elevation, slope, relief, and landform <br />characteristics, as well as roads, buildings, and other cultural features. <br />The most common and highest quality topographic maps of Colorado are those <br />made and sold by the United States Geological Survey. One hundred percent of <br />the state has been mapped, much of it with very high quality 7 1/2' (1:24,000) <br />maps. USGS maps come in several scales: 1:24,000 quadrangles; 1:62,500 <br /> <br />- 17 - <br />