Chapter 10: Navigation

 

Objectives

o       Determining distances (p. 161)

o       Contour lines (p. 144)

o       True north (p. 151)

o       Grid north and magnetic north (p. 145)

 

I. Resources

PowerPoint slides, Chapter 10

 

II. Teaching Points

 

A. Geographic mapping (p. 145)

1.      Plotting points on the globe

2.      Uses addresses or specific geographic locations as descriptive points

3.      Requires little or no training and is easily learned

4.      Best suited for novices

 

B. Geographical coordinate system (p. 146)

  1. Latitude and longitude: parallels of latitude and meridians of longitude
    1. On some maps, the meridians and parallels appear as straight lines.
    2. On most modern maps, the meridians and parallels appear as curved lines.
    3. 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.
    4. Map projection:

                                                               i.      System used to portray a part of the round earth on a flat surface

    1. Geographic coordinate system (latitude and longitude)

                                                               i.      Uses a grid system that covers the entire globe

                                                             ii.      Uses lines of longitude that run north-south, and latitude lines that run east-west

                                                            iii.      Not nearly as effective for ground personnel as it is for those that do not require as much accuracy (boats, aircraft, etc.)

                                                           iv.      Works well when coordinate information must be exchanged between air and ground forces or between international units

    1. Prime meridian

                                                               i.      A line from pole to pole forming a half-circle passing through Greenwich, England

                                                             ii.      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.

    1. International Date Line

                                                               i.      180-degree mark from prime meridian

                                                             ii.      At this line, another meridian is formed that connects with the prime meridian.

    1. Latitude starts at the equator, considered zero, with a circle that encompasses the entire globe between both poles.
    2. The angular distance north or south of the equator is measured in degrees with 90 being the maximum at each pole.
    3. One degree equals 60 minutes.
    4. 1 minute equals 60 seconds.
    5. Plotting a point within 1 navigational second is accurate to within approximately 1000 square feet.
    6. 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)

  1. Special grid for military use
    1. The world is divided into 60 north-south zones, each covering a strip 6° wide in longitude.
    2. 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.
    3. The conterminous 48 United States are covered by 10 zones.
    4. Coordinates are measured north and east in meters (1 meter = 39.37 inches)
    5. Northing values are measured continuously from zero at the equator.
    6. To avoid negative numbers for locations south of the equator, it was assigned an arbitrary false northing value of 10,000,000 meters.
    7. Central meridian through the middle of each 6° zone is assigned an easting value of 500,000 meters.
    8. UTM grid lines are indicated at intervals of 1,000 meters either by blue ticks in the margins or by full grid lines.
    9. Each tick mark is represented by four numbers.
    10. The first two numbers are in superscript¾these represent the 1,000,000- and 100,000-meter grids.
    11. The last two numerals represent the 10,000- and 1000-meter grids.
    12. Computer programs exist that can convert UTM to latitude and longitude.
    13. Most GPS can switch between UTM and latitude/longitude.

 

  1. To use the UTM grid
    1. Place a transparent grid overlay (“interpolator”) on the map to subdivide the grid.
    2. Distances can be measured in meters at the map scale between any point and the nearest grid lines to the south and west.
    3. The northing of the point is the value of the nearest grid line south of its distance north of that line.
    4. 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) (p. 148)

  1. History
    1. Developed in Washington State in the mid 1960s
    2. Wwidely used prior to the proliferation of inexpensive, handheld GPS devices
    3. Designed to help air and ground operations in communicating location information accurately and quickly
    4. UTM and the geographic coordinate system have almost completely supplanted UMS.
  2. UMS is a system that uses letters and numbers to describe points.
  3. 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 Force
  4. Also keyed into 15-minute topographical maps
  5. Difficult to teach and apply in the field

 

E. Township and Range: U.S. Public Land Survey (p. 148)

  1. History
    1. In 1785, the U.S. Public Land Survey was started with the territories northwest of the Ohio River as a test area.
    2. Land was divided into townships six miles square with boundaries running north, south, east, and west.
    3. Townships were to be subdivided into 36 numbered sections of one square mile (640 acres) each.
    4. Principal meridians and baselines were established as a reference system for the township surveys.
    5. The intention was to survey all areas in the United States, thereby setting a national mapping standard.
  2. The surveys were not entirely completed and thus the system is not applicable to many parts of the United States.
  3. Not all USGS maps have township and range lines on them.
  4. SAR personnel should not use these lines because they do not always run true north-south or true east-west as originally intended.

 

F. San Diego Mountain Rescue Team (SDMRT) System (p. 149)

  1. Uses a system to describe a point on a map that is simple, fast, and easy to learn
  2. Because this system is useless without a map, it cannot be strictly considered a method of absolute navigation.
  3. Using the system
    1. Identify the map to be used by scale and quadrant name.
    2. A measuring device such as a ruler is required to measure the point from the nearest borders.
    3. The coordinates are read by simply indicating the distance, in inches, from the left margin and the distance from the bottom margin.
    4. Make sure any measurements are taken from the map margin and not the edge of the map.

 

 

G. Topographical maps (p. 151)

1.      Portrays 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.

a.       Have quadrangle dimensions of 7.5 minutes latitude and longitude, the bounding parallels and meridians being integral multiples of 7.5 minutes

b.      USGS maps are supposed to be updated every 5-10 years.

c.       7.5-minute series maps are the most commonly used maps in ground SAR.

d.      Available as digital files on CD-ROM computer disk

e.       Top of USGS maps is always true north.

f.        The space outside the margin line identifies and explains the map.

g.       Marginal information corresponds to the table of contents, tells how the map was made, where the quadrangle is located, what organizations are responsible for the contents, etc.

h.       Each map is identified in the upper right margin by its quadrangle name, state, or states in which it is located, series, and type.

i.         Usually named after a prominent, immovable place or landmark within the mapped area

j.        The “series” refers to the area mapped in terms of minutes or degrees.

k.      “Type” is either topographic or planimetric.

l.         Title block in the lower right margin shows the quadrangle name, state name, and the geographic index number.

m.     Adjoining quadrangle names are shown in the margin so that users know the adjacent areas.

n.       Geographic coordinates are shown at all four map margin corners and along the margin lines at 2.5-minute intervals for 7.5-minute maps.

o.      Credit legend is located in the lower left margin.

p.      Magnetic declination for the year of field survey or revision is determined to the nearest 0.5 degree from the latest isogonic chart.

q.      Magnetic declination indicates the angular relationship between true north, grid north, and magnetic north.

2.      The center lower margin

a.       Publication scales expressed as a ratio

b.      Bar scales (distance determination)

c.       Contour-interval statement (represent relative elevation)

d.      Vertical datum

e.       Depth-curve sounding statement

f.        Shoreline and tide-range statements

g.       Map accuracy statements

 

3.      Trails are not included in the legend unless there are no roads on the map.

4.      The year of the data shown on the map is printed beneath and as part of the title in the lower right margin.

5.      Generally there are six colors on the map.

a.       Brown: Contour lines

b.      Green: Vegetation

c.       Blue: Water

d.      Black: Manmade objects

e.       Red: Roads and built-up areas

f.        Purple: New changes or updates

 

6. Contour lines

    1. Each contour line connects all points at the same elevation above sea level.

f.        Three types of contour lines

                                                               i.      Index: Darker line with numbers superimposed on it, indicating the elevation along that particular line

                                                             ii.      Intermediate: Lighter brown lines, fall between index lines and are not numbered

                                                            iii.      Supplementary: Dashed lines that may be used when the terrain is very flat and there are large distances between contour lines

    1. Every fifth contour line is called an index interval.
    2. Contour lines that touch indicate a cliff
    3. Widely spaced contour lines indicate a gentle slope or flat terrain.

 

7. Terrain features

    1. Ridgeline

                                                               i.      All terrain features evolve from a complex landmass known as the “ridgeline.”

                                                             ii.      Ridgeline should not be confused with a ridge.

                                                            iii.      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.

                                                           iv.      A ridge is simply one of the terrain features that may arise from a ridgeline.

    1. A total of ten natural or manmade features may arise from a ridgeline.
    2. Two categories of ridgelines:

                                                               i.      Major: hill, saddle, valley, ridge, depression

                                                             ii.      Minor: draw, spur, cliff, cut/fill

 

 

H. Compass (p. 158)

  1. Two styles
    1. Orienteering (clear base plate)¾preferred compass for SAR
    2. Lensatic (military)

 

  1. Characteristics of a quality compass for SAR
    1. Base plate or base
    2. Bezel, dial, ring, or compass housing
    3. Bearing/orienting lines
    4. Magnetic needle
    5. Direction of travel arrow
    6. Index line or lubber line
    7. Sighting mirror
  2. Navigating with a compass
    1. Good compass posture:

                                                               i.      Stand still with arms comfortably at your sides.

                                                             ii.      Bend elbows so that both hands can hold the compass directly in front of your body.

                                                            iii.      Hold the compass either at chest-level or belt-level.

                                                           iv.      Ensure that the direction of travel arrow is pointing in the same direction as your toes.

                                                             v.      When you move the compass to a specific heading, move your entire body as a solid extension.

                                                           vi.      Hold the compass level so that the needle may move freely.

 

I. Following a heading (p. 160)

  1. 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.
  2. 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 object.
  3. Reconfirm your heading to the object, lower your compass, and start walking to the object.
  4. Traveling a long distance on a compass bearing can be challenging but gets easier with practice.

 

J. Using a map and compass together (p. 160)

  1. The compass is used primarily as a protractor and ruler.
  2. 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.
  3. When using the compass as a protractor, the magnetic needle can be completely ignored.
  4. 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.
  5. Then turn the dial ring until the orienting arrow, with the arrow pointing north, is parallel to the nearest north-south meridian.
  6. The scales on the bottom margin of the map can be used to measure distance on the map.
  7. 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)

  1. Magnetic declination
    1. The angle between the direction the magnetic needle points and true north
  2. Agonic line
    1. The line along which a compass needle points to both true north and magnetic north
    2. East of the agonic line, a compass needle will point west of true north.
    3. West of the agonic line, a compass needle will point east of true north.
  3. If you know the magnetic declination of the area in which you will be navigating, you have four options:

a.       Ignore it: When using a compass without a map, operating on the agonic line

b.      Adjust 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.

c.       Adjust 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.

d.      Adjust 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 to map.

 

L. Measuring distance by stride: “Tally” (p. 165)

1.      Distance can be estimated by knowing the length of one’s stride and multiplying it by the number of strides walked.

2.      The English term “mile” is derived from a Roman term meaning “1000 Roman Paces” or double steps.

3.      One step is the distance one walks when measured from one foot to the other.

4.      A 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.

5.      Measuring your stride is sometimes referred to as finding your “tally.”

 

M. Global Positioning System (p. 166)

  1. A space-based radio navigation system consisting of a constellation of satellites and a network of ground stations used for monitoring and control
  2. A minimum of 24 GPS satellites orbit the Earth.
  3. The principal behind GPS is the measurement of distance (or range) between the receiver and the satellites.
  4. Limitations of GPS

a.       Requires line-of-sight to the satellites and will not work in all terrain

b.      Should not be used as the sole navigation device

c.       The less than prefect accuracy is not always acceptable, especially for altitude.

d.      Human error

e.       Position display can easily be misread.

f.        Typical battery life of most GPS units is between 4 and 6 hours.