Map, Compass & GPS

Map, Compass & GPS
Wild flowers along Fall Creek on the way to the Green Lakes - Oregon

Monday, June 24, 2013

Topographic Map Scale defines map scale as:

“A ratio which compares a measurement on a map to the actual distance between locations identified on the map.”


A topographic (topo) map’s scale information is located at the bottom center of the map.  Other maps will generally have scale information in the large map key that outlines many of the features and data printed on the map.


The map scale for a United States Geologic Survey (USGS) 7.5 topo minute map is highlighted below.




A closer look of the scale information:


 The area circled in red is the ratio discussed by  Note that the ratio has no units of measurement assigned (e.g., feet, meters, acres.)

 But, if you add measurements to both sides the ratio value becomes more meaningful.  For example:

                                                       1inch :  24,000 inches

 This now means that 1inch of measurement equals 24,000 inches on the map.

 Divide the 24,000 inches by 12 inches (one foot) the ratio value now becomes:

                                                        1 inch = 2000 feet

There are many other maps produced by government agencies (federal and state), parks and private companies.  There are also many scale options to be found too.  Some maps will use similar ratios such as 1:250,000 while others will simply state: 1inch = 2 miles.  Here is another example; below.


The bar scales (see above) provide the best visual representation of scale.  The bar scales provide data in miles, kilometers, nautical miles or feet.  Notice the small graduations to the left of each scale.  In the case of the kilometer scale, the graduations are in units of 1000 meters.  This gives you the detail for measuring distance on a map.

For the backcountry hiker the USGS topo 7.5 minute topo (scale of 1:24,000) is your best source of information.   At this scale, the map has much more validity and provides more usable information for your backcountry planning.  You can view important landmarks, streams and geographic features.

To complete the navigation picture I always refer a second map, such as a map of the national forest (e.g., the Deschutes National Forest.)  Commonly, such a map will be “zoomed” way out and have a scale of 1:100,000 or 1:250,000.  Imagine that such a map would be made up of many 7.5 minute quadrangles.

Other options are available to the hiker.  For example DeLorme produces an atlas and gazetteer for every state; visit National Geographic has excellent 1:24,000 scale maps for many of the national parks.  My most recent map came on waterproof paper and was very up to date.  My favorite product is made by and is the mapping software Terrain Navigator.  I’ve been using this software in its various releases since 1998.  Terrain Navigator allows the hiker to up load/down load waypoints and tracks from many GPS receivers, has tools for backcountry planning, provides several map scale and zoom options and is very simple to use.

 Finally, I pack my map into a 1 gallon zip lock bag with my compass and GPS.  Never leave home without this trio.

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