Chapter 10: Navigation
- Define the following terms or concepts:
Determining distances (p. 161)
Contour lines (p. 144)
True north (p. 151)
Grid north and magnetic north (p. 145)
- Demonstrate the use of the UTM (Universal Transverse
Mercator) Grid System to determine the coordinates for a given point. (p.
- Describe the procedures used to obtain a back
azimuth. (p. 158-160)
- Describe how to take a bearing in the field and
transfer it correctly to the map, and obtain a bearing on the map and transfer
it correctly to the field. (p. 164-165)
- Describe techniques used to navigate during daylight
hours while wearing a 24-hour pack. (p. 151-165)
- List three advantages and three limitations of GPS
(Global Positioning System) units as employed during search operations.
PowerPoint slides, Chapter 10
II. Teaching Points
A. Geographic mapping (p. 145)
points on the globe
addresses or specific geographic locations as descriptive points
little or no training and is easily learned
suited for novices
B. Geographical coordinate system
- Latitude and longitude: parallels of latitude and
meridians of longitude
- On some maps, the meridians and parallels appear as
- On most modern maps, the meridians and parallels
appear as curved lines.
- These differences are due to mathematical treatment
required to portray a curved surface on a flat surface so that important
properties of the map such as distance are shown with minimum distortion.
- Map projection:
System used to portray a part of the round earth on a flat
- Geographic coordinate system (latitude and
Uses a grid system that covers the entire globe
Uses lines of longitude that run north-south, and latitude
lines that run east-west
Not nearly as effective for ground personnel as it is for
those that do not require as much accuracy (boats, aircraft, etc.)
Works well when coordinate information must be exchanged
between air and ground forces or between international units
- Prime meridian
A line from pole to pole forming a half-circle passing through
From the prime meridian, considered zero, the angular distance
east or west is measured by an angle in degrees up to 180 in either direction.
- International Date Line
180-degree mark from prime meridian
At this line, another meridian is formed that connects with
the prime meridian.
- Latitude starts at the equator, considered zero,
with a circle that encompasses the entire globe between both poles.
- The angular distance north or south of the equator
is measured in degrees with 90 being the maximum at each pole.
- One degree equals 60 minutes.
- 1 minute equals 60 seconds.
- Plotting a point within 1 navigational second is
accurate to within approximately 1000 square feet.
- Very difficult to define 1 second (1.3 mm) on a 7.5
minute map; 15-second accuracy is much more realistic.
C. Universal Transverse Mercator
System (p. 146)
- Special grid for military use
- The world is divided into 60 north-south zones,
each covering a strip 6° wide in longitude.
- Zones are numbered consecutively beginning with
Zone 1, located between 180° and 174° west longitude, and progressing
eastward to Zone 60, between 174° and 180° east longitude.
- The conterminous 48 United States are covered by 10
- Coordinates are measured north and east in meters
(1 meter = 39.37 inches)
- Northing values are measured continuously from zero
at the equator.
- To avoid negative numbers for locations south of
the equator, it was assigned an arbitrary false northing value of
meridian through the middle of each 6° zone is assigned an easting
value of 500,000 meters.
- UTM grid lines are indicated at intervals of 1,000
meters either by blue ticks in the margins or by full grid lines.
- Each tick mark is represented by four numbers.
- The first two numbers are in superscript¾these
represent the 1,000,000- and 100,000-meter grids.
- The last two numerals represent the 10,000- and
- Computer programs exist that can convert UTM to
latitude and longitude.
- Most GPS can switch between UTM and
- To use the UTM grid
- Place a transparent grid overlay (“interpolator”)
on the map to subdivide the grid.
- Distances can be measured in meters at the map
scale between any point and the nearest grid lines to the south and west.
- The northing of the point is the value of the
nearest grid line south of its distance north of that line.
- Easting is the value of the nearest grid line west
of it plus its distance east of that line.
D. The Uniform Mapping System (UMS)
- Developed in Washington State in the mid 1960s
- Wwidely used prior to the proliferation of
inexpensive, handheld GPS devices
- Designed to help air and ground operations in
communicating location information accurately and quickly
- UTM and the geographic coordinate system have
almost completely supplanted UMS.
- UMS is a system that uses letters and numbers to
- Tied into Sectional Aeronautical Charts (1:500,000)
that are broken down into a grid and used by Civil Air Patrol and U.S. Air
- Also keyed into 15-minute topographical maps
- Difficult to teach and apply in the field
E. Township and Range: U.S. Public
Land Survey (p. 148)
- In 1785, the U.S. Public Land Survey was started
with the territories northwest of the Ohio River as a test area.
- Land was divided into townships six miles square
with boundaries running north, south, east, and west.
- Townships were to be subdivided into 36 numbered
sections of one square mile (640 acres) each.
- Principal meridians and baselines were established
as a reference system for the township surveys.
- The intention was to survey all areas in the United
States, thereby setting a national mapping standard.
- The surveys were not entirely completed and thus the
system is not applicable to many parts of the United States.
- Not all USGS maps have township and range lines on
- SAR personnel should not use these lines because they
do not always run true north-south or true east-west as originally
F. San Diego Mountain Rescue Team
(SDMRT) System (p. 149)
- Uses a system to describe a point on a map that is
simple, fast, and easy to learn
- Because this system is useless without a map, it
cannot be strictly considered a method of absolute navigation.
- Using the system
- Identify the map to be used by scale and quadrant
- A measuring device such as a ruler is required to
measure the point from the nearest borders.
- The coordinates are read by simply indicating the
distance, in inches, from the left margin and the distance from the
- Make sure any measurements are taken from the map
margin and not the edge of the map.
G. Topographical maps (p. 151)
the shape and elevation of the terrain while showing a graphic representation
of selected manmade and natural features on a part of the Earth’s surface
plotted to a definite scale.
quadrangle dimensions of 7.5 minutes latitude and longitude, the bounding
parallels and meridians being integral multiples of 7.5 minutes
maps are supposed to be updated every 5-10 years.
series maps are the most commonly used maps in ground SAR.
as digital files on CD-ROM computer disk
of USGS maps is always true north.
The space outside the margin line identifies and explains the
information corresponds to the table of contents, tells how the map was made,
where the quadrangle is located, what organizations are responsible for the
map is identified in the upper right margin by its quadrangle name, state, or
states in which it is located, series, and type.
Usually named after a prominent, immovable place or landmark
within the mapped area
The “series” refers to the area mapped in terms of minutes or
is either topographic or planimetric.
Title block in the lower right margin shows the quadrangle
name, state name, and the geographic index number.
quadrangle names are shown in the margin so that users know the adjacent areas.
coordinates are shown at all four map margin corners and along the margin lines
at 2.5-minute intervals for 7.5-minute maps.
legend is located in the lower left margin.
declination for the year of field survey or revision is determined to the
nearest 0.5 degree from the latest isogonic chart.
declination indicates the angular relationship between true north, grid north,
and magnetic north.
center lower margin
scales expressed as a ratio
scales (distance determination)
statement (represent relative elevation)
Shoreline and tide-range statements
are not included in the legend unless there are no roads on the map.
year of the data shown on the map is printed beneath and as part of the title
in the lower right margin.
there are six colors on the map.
Roads and built-up areas
Purple: New changes or updates
6. Contour lines
- Each contour line connects all points at the same
elevation above sea level.
Three types of contour lines
Index: Darker line with numbers superimposed on it, indicating
the elevation along that particular line
Intermediate: Lighter brown lines, fall between index lines
and are not numbered
Supplementary: Dashed lines that may be used when the terrain
is very flat and there are large distances between contour lines
- Every fifth contour line is called an index
- Contour lines that touch indicate a cliff
- Widely spaced contour lines indicate a gentle slope
or flat terrain.
7. Terrain features
All terrain features evolve from a complex landmass known as
Ridgeline should not be confused with a ridge.
A ridgeline is a line of high ground usually with variations
in elevation along its top and low ground on all sides, which is the source of
many terrain features.
A ridge is simply one of the terrain features that may arise
from a ridgeline.
- A total of ten natural or manmade features may
arise from a ridgeline.
- Two categories of ridgelines:
Major: hill, saddle, valley, ridge, depression
Minor: draw, spur, cliff, cut/fill
H. Compass (p. 158)
- Two styles
- Orienteering (clear base plate)¾preferred
compass for SAR
- Lensatic (military)
- Characteristics of a quality compass for SAR
- Base plate or base
- Bezel, dial, ring, or compass housing
- Bearing/orienting lines
- Magnetic needle
- Direction of travel arrow
- Index line or lubber line
- Sighting mirror
- Navigating with a compass
- Good compass posture:
Stand still with arms comfortably at your sides.
Bend elbows so that both hands can hold the compass directly
in front of your body.
Hold the compass either at chest-level or belt-level.
Ensure that the direction of travel arrow is pointing in the
same direction as your toes.
When you move the compass to a specific heading, move your
entire body as a solid extension.
Hold the compass level so that the needle may move freely.
I. Following a heading (p. 160)
- Once you have selected a heading, point your toes in
the direction that you wish to travel and sight a prominent immovable
object in the distance.
- Once you confirm the object, close your eyes for just
a few seconds, then open them just to reconfirm that you can easily find your
- Reconfirm your heading to the object, lower your
compass, and start walking to the object.
- Traveling a long distance on a compass bearing can be
challenging but gets easier with practice.
J. Using a map and compass together
- The compass is used primarily as a protractor and
- 360-degree dial, in association with the orienting
lines in the base of the bezel, serve as the protractor. The straight
sides of the base plate serve as a straight edge.
- When using the compass as a protractor, the magnetic
needle can be completely ignored.
- To determine the heading from one point to another on
the map, place the compass on the map so that one edge of the base plate
touches both the starting point and the destination with the direction of
travel arrow pointing in the direction of the destination.
- Then turn the dial ring until the orienting arrow,
with the arrow pointing north, is parallel to the nearest north-south
- The scales on the bottom margin of the map can be
used to measure distance on the map.
- On a 1:24000 scale map, one inch on the map equals
24,000 inches or 2000 feet in the terrain.
K. Adjusting for magnetic
declination (p. 161)
- Magnetic declination
- The angle between the direction the magnetic needle
points and true north
- Agonic line
- The line along which a compass needle points to
both true north and magnetic north
- East of the agonic line, a compass needle will
point west of true north.
- West of the agonic line, a compass needle will
point east of true north.
- If you know the magnetic declination of the area in
which you will be navigating, you have four options:
it: When using a compass without a map, operating on the agonic line
for it on the compass: Some compasses have a small screw that allows the user
to adjust for declination; this offsets the orienting arrow and index line in
the base of the bezel just enough to compensate for declination when the
compass is used as a protractor with a map.
for it by drawing magnetic meridians (north-south lines) on the map: Adding
these lines requires a protractor, long straight edge, and the angle of
declination. Not recommended for SAR due to the difficulty in accomplishing
this manually. Added lines may make the map more difficult to read.
for it mathematically: You must know if declination is east or west. Look at
the declination diagram at the bottom margin of the map. If “MN” is to the left
of the star, the declination is west. If “MN” is to the right of the star, the
declination is east. Determine if you are going from map to compass or compass
L. Measuring distance by stride:
“Tally” (p. 165)
can be estimated by knowing the length of one’s stride and multiplying it by
the number of strides walked.
English term “mile” is derived from a Roman term meaning “1000 Roman Paces” or
step is the distance one walks when measured from one foot to the other.
stride is equivalent to two steps or the distance between where one foot
strikes the ground and where the same foot strikes the ground again.
your stride is sometimes referred to as finding your “tally.”
M. Global Positioning System (p.
- A space-based radio navigation system consisting of a
constellation of satellites and a network of ground stations used for
monitoring and control
- A minimum of 24 GPS satellites orbit the Earth.
- The principal behind GPS is the measurement of
distance (or range) between the receiver and the satellites.
- Limitations of GPS
line-of-sight to the satellites and will not work in all terrain
not be used as the sole navigation device
less than prefect accuracy is not always acceptable, especially for altitude.
display can easily be misread.
Typical battery life of most GPS units is between 4 and 6