navigating a topographical map

7/29/2019 Navigating a Topographical Map

1/3

Navigating a Topo Map

Do topographical maps seem confusing? Do you view most maps as a mass of

squiggles, color splotches and undecipherable gibberish, with terms like: datum,

UTM, WGS84.

A map and compass are vital land navigation tools, but you must first know how to

read the map!

Reviewing a topographic map is usually the starting point for the planning of any

back country trip. A topographic map is your road map to the outdoors. It provides

you detailed information at a scale that is meaningful and detailed. For years, the

US Geologic Survey (USGS) has been the principal publisher of accurate maps.

Within the last decade we have seen many innovations in mapping products thatinclude new mapping companies and publishers, software, maps for the GPS, and

Apps for the iPhone. Still, the USGS map remains the standard for back country

navigation (visit the USGSs site at www.topomaps.usgs.gov.) Id also recommend

looking at June Flemings Staying Found: The Complete Map and Compass Handbook

or Bjorn Kjellstroms Be Expert with Map and Compass. Once you develop a map

foundation you will easily shift to many of the other products on the market today.

Many publications, videos, and web sites will give you a complete rundown on the

features, symbols and components to a map. This article will discuss a few of the

key features that you should be aware of on a 7.5 minute map.

Scale Consider scale as your view of the map; it is like your overhead zoom

setting. To cut to the chase, a 7.5 minute map or quadrangle has a scale that is

referred to as 1:24,000; where one inch is equal to 2000 feet. It is your best

source of information of the back country. At this scale, the map has much more

validity and provides more usable information for 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.

North Features on a map such as trails, roads, mountain peaks and streams are all


2/3

laid out in relation to true North; the North Pole. The north-south borders of the

map and the small declination diagram are your best references for true North.

Other grid lines (such as the red Township, Section and Range lines) may not be

aligned to true north at all. Be careful of these lines should you need to triangulate

your position on a map.

Declination This is the angular difference between true North and Magnetic

North. The red needle on your magnetic compass points to Magnetic North. The

accuracy of the information found in the Declination Diagram is dependent on the

age of the map. To get the latest declination for any area visit www.magnetic-

declination.com.

Personally, I use a magnetic compass that can be adjusted for declination; it just

makes navigation easier. When adjusted, my compass provides bearing informationin degrees true north as does my map and my adjusted GPS.

Coordinates Latitude and Longitude (Lat/Long) are the familiar coordinate system

to most people. Coordinate data is found at the top and bottom corners of each

map. Lat/Long coordinate increments are also found every 2 (minutes) and 30

(seconds) on the sides of the Map. A scaling device is necessary to pull complete

coordinates off a map: (This is a pain!)

In the 1940s a coordinate system know as Universal Transverse Mercator (UTM)

was developed. To keep a very long story short, your 7.5 minute map has a new grid

laid over it, and the grid dimensions are 1000 meters by 1000 meters. For more

complete information on UTM grid visit the USGSs web site UTM or Lathems GPS

Made Easy (GPS Made Easy: Using Global Positioning Systems in the Outdoors).

Simplicity is the essence of UTM. Scouts, hunters and hikers have joined Search

and Rescue (SAR) teams around the country in using this system. Your GPS

receiver can easily be switched to UTM from the set-up menu.

Bar Scales Notice the bar scales at the bottom of the 7.5 minute map. The scales

provide measuring data in miles, feet and meters. On the far left side of the meter

scale, the scale is broken down into units of 100 meters, this applies directly to

UTM.

Notice on the scale bar (feet) that 1 inch equals 2000 feet. This topographic map

scale of 1:24,000 is your best source of information of the back country. At this

scale, the map has much more validity and provides more usable information for you
http://www.magnetic-declination.com./http://www.magnetic-declination.com./http://www.magnetic-declination.com./http://www.magnetic-declination.com./


3/3

backcountry planning.

Map Datum Information about map datum is found in the lower left corner of a

7.5 minute map. The simplest definition of datum from Garmin GPS: A math model

which depicts a part of the surface of the earth. Latitude and longitude lines on apaper map are referenced to a specific map datum. The map datum selected on a

GPS receiver needs to match the datum listed on the corresponding paper map in

order for position readings to match. The bottom line: Most 7.5 minute maps are

made to the North American datum of 1927 (NAD27 or NAD27 CONUS on your

GPS). New GPS receivers are set to datum WGS84. The difference between the

datum could be over 100 meters/yards. The solution: When pulling points off a map

shift your GPSs datum to match the map. If precision is not an issue for your

outing dont worry about datum.

As you begin your trip planning dont forget the magnetic compass, the important

partner to any topographic map.

Arise ye workers from your slumber.

Arise you prisoners of want

For reason and revolt now thunders,

And at last ends the age of cant.

Away with all your superstitions.

Servile masses arise, arise!

Well change henceforth the red tradition,

And spurn deaths dust to win the prize.

So comrades come rally,

And the protracted fight, let us face!

We will destroy the parasites and their bosses,

The Right unites the European race.

We will vanquish the evil parasitesBy the only way it can be done

No quarter is our standard

And we fight beneath the blood Red Sun

By J. Martin

navigating a topographical map

Documents