BACKCOUNTRY
outdoor Leader
skillS
Basic
Map & Compass
Reading a Topo Map
Colors, Symbols, Measuring Distance
& Reading Contours
Basic Assumption for this presentation: is that you
have some basic skills in how to read a map
Map Colors
• Green – Vegetation
• Blue - Water
• Red Lines - Major roads
• Black Objects - Manmade objects
• White - Lack of vegetation
• Brown - Contours and elevation data
• Magenta/Purple - Updates and
revisions, usually by satellite or
aircraft images
Basic Map Symbols
• Roads symbols
• trails
• Water related symbols
• Elevation and contour
related symbols
• Buildings and other man-made
symbols
+
• Vegetation areas &
related symbols
For additional symbols see USGS
Topographic Map Symbols attached
For additional
symbols
see
USGS Topographic Map Symbols
at
end
of
this
document
Document attached
Topo Map Reading Measuring Distance
The scale of a topographic map .appears like this
There are generally two types of Scales presented,
a ratio scale, and a graphic bar scale. The scales allow
measurement of distances on the map and
conversion to real-world distances. The contour
Interval is presented with the scales
Topo Map Reading - Distance
Topographic (and other maps as well) come in a variety of scales. The
scale of the map is determined by the amount of real-world area
covered by the map.
For example, 7.5 minute topographic quadrangles put out by the U.S.
Geological Survey have a scale of 1:24,000. This type of scale is known
as a ratio scale
What is a ratio scale? Basically that one inch on the map is equal to
24,000 inches (or 2000 ft) in the real world.
Measuring Distance – Ratio Scale
it means that one of anything (cm, foot, boot print, etc.) on the
map is equal to 24,000 of the same thing on the earth. Another
way of writing this would be a fractional scale of 1/24,000,
means that objects on the map have been reduced to
1/24,000th of their original size.
If that is your boot print on the map, and it is 12” long, how far is it
from Gunston Rd to the waters edge in Pohick Bay using the dirt road ?
# 0f boot lengths x12”x 24000 .6 X12”x24000= 576,000” @ 2.7 miles
Topo Map Reading
Contours & Terrain
Reading Contours
•
•
•
•
Contour lines show terrain features & elevation
Index and intermediate contour lines
– A Index line has the elevation marked on the line,
and are darker
– Intermediate Contours are lighter and do not
indicate a elevation
Contour interval – It is noted with the Map Scales
– Usually 20 ft. Be careful a lot of western maps are
at 100 ft intervals. The contour interval is the
elevation change between contour lines
Visualizing elevation change between contour lines on
the map is represented by the photo below
– Close distance ==> steep terrain
– Farther apart ==> flatter terrain
Reading Contours
Match Game
Reading Contours
Match Game
TERRAIN AWARENESS
Visualizing
CONTOUR 3d PROFILES
Visualizing a topo map in 3D takes
experience and can easily be demonstrated
in the field. This skill is called Terrain
Awareness
X
Exercise: What do you see in your mind when
you visualize the above 2D image
from vantage point X?
Visualizing
CONTOUR 3d PROFILES
How was your vision?
Knuckle Contour
Demonstration
Simple way to show
Transition from 2D to 3D
DO NOT USE SHARPIES
Topo Map Reading – True North
Magnetic North and Declination
The declination for the map can be
found in the legend of the map.
The angle of declination is the angle
between true north and magnetic north.
For our area it is 9 to 11 degrees west
“negative” The angle is not constant and
Changes overtime.
Declination? What is it?
• The Difference between geographic
north (true north) and magnetic north
What is the cause of this deviation?
The north magnetic pole of the earth is
not at the “north pole”
It is offset, so therefore your compass
does not point to true north
Topo Map Reading – Declination
How do you correct for it – Easy…Correct Your Map
More difficult – Correct your Compass, more later
Mag N-S
True N-S
Topo Map Reading – Declination
Correcting your map
Draw a line at same angle
as the magnetic north arrow
in the map index. Continue
to draw lines parallel to that
line across the map.
Mag N-S
Correcting your map
eliminates the need to
adjust your compass or
Mentally correct your
Readings taken off the
map
True N-S
Basic Compass Use
Basic Assumption:
You have a basic understanding of how a
compass works
Parts of the Compass
bezel
USING A COMPASS – Basic Skills
Shooting an Azimuth:
First- What is an Azimuth?? The Professor’s
definition
Azimuth: is an angular measurement in a
spherical coordinate system.
A vector from an observer (origin) to a point of
interest is projected perpendicularly onto a
reference plane; the angle between the
projected vector and the reference vector on
the reference plane is called the azimuth.
Simply put:
Turn Bezel so the angle in degrees from north
that you want to travel are aligned with the
direction of travel arrow. If you want to go
northwest that would be 315 degrees
Shooting an Azimuth:
Simply put - continued:
With the Bezel set at 315 degrees hold the
compass flat in your hand with the direction of
travel arrow pointing forward.
Now rotate yourself (your body) around so
that the north end (the red end) of the
compass needle is completely inside the
orienteering arrow, the “dog house”.
The line of travel arrow is now pointing you on a 315
degree heading or azimuth. Sight an unobstructed target
that is in the line of sight of the direction of travel arrow.
As you walk to this target you will be on a compass
heading of 315 degrees.
Using Map & Compass
Together - Orienting a Map
A Map is Oriented if:
The Terrain Features of the map are
aligned with features of the
landscape (Terrain Awareness)
How is this done?
Easy Method - With Corrected
Magnetic N-S lines drawn on map:
1.Set bearing on compass to 0o
2.Align baseplate with Magnetic
N-S lines
3.Turn map & compass until needle
is over orienting arrow in
compass housing (bezel)
Orienting a Map, cont’d
•
Without Magnetic N-S lines – (DIFFICULT)
1. Set compass bearing to 350o (this is
to correct for a10 degree west declination, if its is
12 degree west then set to 348, etc.)
2. Align baseplate with True N-S
lines
3. Turn map & compass until needle
is over orienting arrow in housing
• Without Magnetic N-S lines but with a
aacompass that has adjustable declination
1. Adjust compass declination to
10o E
2. Set bearing to 0o
3. Align baseplate with True N-S
lines
4. Turn map & compass until
needle is over arrow in housing