Mazamas Wilderness Navigation class handouts

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Why is a map more important than a compass? There are FOUR main components of navigation, and maps tell you ALL of them. 1. Distance (How far is the approach hike to base camp?) 2. Elevation (What’s the elevation gain to the summit?) 3. Terrain (Steep or flat? Gully or ridge? Dense forest or open snow?) 4. Direction (If we head NW from here, we’ll find the trail ) A map can tell you all of these. A compass cannot tell you distance, elevation, or terrain. A compass is only used when you need more precise direction, such as “the saddle on the ridgeline we are trying to hit is 310° from camp”. Unless you want to walk in a straight line, a compass is next to useless without a map. Maps – an overview What’s a “topo” map? - Symbols & Legend - Datum - Declination - Scale - Coordinate systems Lat-Long vs. UTM - Contour lines Topographic maps show four main things: 1) Contours (elevation), 2) Water features, 3) Vegetation 4) Manmade features (roads, trails). What’s a 7½ minute maps? • The entire USA (outside of Alaska) is mapped at a scale of 1:24,000, and printed on a sheet showing with 7.5 minutes of longitude and 7.5 minutes of latitude, about 6 by 9 miles. This is the most detailed and consistent base map of the country. • These were the only good maps available for a long time. • Nowadays, many private companies (like Green Trails or Nat Geo Topo software) have taken the free government base map data and made the maps more user-friendly for backcountry use by highlighting trails, adding a clear UTM grid and a more useful legend. Therefore, using an actual 7½ minute map in the backcountry is becoming a thing of the past. 3 cautions on using mapping software 1. Major features may be missing, depending on the date of the air photos used for the base map (example: no Hwy 20 in the WA Cascades?!) 2. The map scale can be whacky; there’s no standard. 3. Useful information in the margins of printed maps may be missing. Map Legends • Most maps do not have complete legends, esp. map printed from mapping software. • Universal legend standards do not exist, so symbols or colors are not alike on all maps. 2
Map Datums • A map datum is a model of the earth used by surveyors. Your GPS has LOTS to choose from! • Earlier datums were based on surveyed points. Newer ones are based on satellite measurements. One is not “better” than another, just different. • Most all US topo maps are based on either NAD-27 or NAD-83. (NAD = North American Datum, 1927 or 1983). Older topo maps are typically NAD-27. • Most GPS units default to a datum “WGS 84”; it’s the same as NAD83. • Do you need to care about datums? Only if you are using a GPS, then the datum on your GPS should be set to the same as your paper map. • If the datums are not the same, you could have a discrepancy of about 200 meters. (Maybe a problem, normally not.) Map Declination - Most maps have a declination diagram that usually looks something like this. You can ignore mils and GN, which means grid north. - Set the adjustable declination on your compass (here 14 degrees east) to match your map, so you can more easily use map and compass together. Map Scale • All printed maps should have either a ratio or a bar scale. Often you’ll have both. • All of USA is mapped at 1:24,000 - a good level of detail for backcountry travel. • Ratio scale: A “1:100,000” scale means the distance between any two map points is 100,000 times longer in the real world. (3.5 cm on map = 3.5 Km on the ground). • Ratio scale is great in metric countries, next to useless in USA Note that a large scale map shows a small area, i.e. more zoomed in. A small-scale map shows a large area, i.e. zoomed out. (This is not very intuitive for some people, me included!) Map measuring tips: 1. Get a sharpie pen, and put small black tick marks on your compass string every 2.6 inches apart. On a 1:24,000 scale map, each tick mark represents one mile. 2. Copy the bar scale onto scrap paper. Use this scrap paper to measure distances. 3. Finger scale: Put your fingers onto the scale bar, and see what finger covers a convenient portion of a mile or a KM, such as “ my thumb width = ½ mile”. Then, measure map distance with your thumb. ``````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````` 3
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Page 5 and 6: Potentially the most important use
Page 7 and 8: Orienting the map • Most of us ho
Page 9 and 10: Download ANY 7.5 minute map for FRE
Page 11: 3. If you are unsure of your locati

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