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Map Notes


  • PDF files

    All the maps on these pages are distributed as PDF files, which can produce very high quality printouts. You will need Adobe Acrobat® Reader (version 4.0 or above) in order to use these files. Version 5.0 with the "smooth line art" option turned on produces a very nice on-screen display. To get the best printed results, use a printer with 600 dpi resolution (or better). A color printer will make them look their best, but they still look good on a black and white laser printer. Even if you don't intend to print them out, downloading the PDF's can still be useful as you can use Acrobat's magnifying glass tool to zoom in on the map for greater detail.

    Get Acrobat Reader




  • Improved Map Quality

    On 10/30/2000, new versions of all the maps were uploaded, with the following improvements:

    • The background base maps now show wooded areas shaded in light green. USGS 1:250,000 scale Land Use Land Cover data was used for this. Because of the small scale of this data, wooded areas don't show up with as much detail as you would find on a typical 1:24,000 scale USGS paper quad map...


    • The lines used to represent roads, trails, and waterways are now weighted according to their class, giving a better feel for their relative sizes.


    • Names of common features (towns, bodies or water, landmarks, etc.) are now shown on the map for better reference. USGS GNIS data was used for this purpose.


    • The maps now feature UTM grid ticks, and a cut-out scale map ruler, enabling accurate positioning and navigation via GPS, or other means.




  • How the maps were made

    The maps were made using Arcview GIS software. The raw data for the maps were obtained from the USGS' EROS Data Center in the form of freely downloadable Digital Elevation Models (DEM's) and Digital Line Graphs (DLG's). Some data were also obtained in the field using a Garmin GPS III+.



  • Map Accuracy

    The elevation data are derived from 30 meter USGS DEM's (1:24,000 scale). Because there is only one elevation data point for every 30 square meters (~100 feet) on the ground, certain tall geological features that are less than 30 meters wide may appear slightly shorter on the map than they are in reality. The positional accuracy of the elevation points is dictated by NMAS (National Map Accuracy Standards) which state that 90% of the data on a map must be within 0.02 inches of it's actual location. For the 1:24,000 scale data used here, that translates to about 12 meters or 40 feet in ground units.

    Most of the roads, trails and streams data are derived from 1:100,000 scale USGS DLG's. According to NMAS, these data are accurate to within about 50 meters or 166 feet in ground units.

    The rest of the roads and trails data were gathered by GPS. The accuracy of GPS data is regulated by the US Department of Defense, and is always within 100 meters, but usually within 50 meters. As of 12/28/1998, the main routes of the Hall Ranch, Horsetooth Mountain Park, and the Georgia Pass rides are based on GPS data.

    For comparison, the width of the line used to show the main routes is roughly 60 meters in ground units. So at the scale depicted in these maps, the accuracy is plenty good enough...



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Last updated Monday, May 08, 2006, 09:09:18 AM, -0400