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 MAPS, COMPASS, AND NAVIGATION


Each rescue member should be able to navigate with a minimum of 300 ft accuracy using a 7.5 min. map and a compass. Each member of SAR should keep available the local 7.5 min quads specified in the team personal equipment list. The team and many members maintain a file of other maps that have proven useful in and outside of Ventura county. This chapter attempts to explain the technical aspects of maps, the use of a compass, and the use of map and compass to navigate. In addition to the technical aspects of map reading, there is a skill which allows an individual to translate a 2 dimensional map representation into a visual image of the terrain. This skill of terrain orientation is an art which some find easier than others but must be practiced to maintain a high level of efficiency.  

In dealing with map and compass, one will need to be able to correlate the terrain to the map symbols and directions, be able to choose a path on a map, and follow that path in the actual terrain, be able to derive a compass heading from measurements on a map and translate that reading to a compass heading useful in the field, and likewise measure a bearing in the field and apply that measurement to a map. In addition the rescue member should be able to locate positions in the field using "Dead Reckoning" navigation.  

In addition to classical map and compass technique, the team also uses satellite navigation systems based on the Global Positioning Systems (GPS). These hand-held and truck-mounted systems calculate position to an accuracy between 20-100 meters. These electronic systems provide a great advantage in the field. However, since electronic systems fail and do not work well in steep canyons, the member must be able to rely on his classical skills.

DEFINITIONS  

Triangulation is the technique of locating one's position by measuring several (at least 2) bearings to different prominent landmarks. The bearings are plotted on a map as a straight line originating at the known landmarks. The intersection of the lines is the current position of the observer. If no error exists in the measurements the location will be a point intersection of the lines, otherwise a variance around a point will exist.  

Dead Reckoning Navigation is a technique of navigating from one location to another by following a compass heading and calculating the total distance traveled (normally by counting paces.)  

MAP PAGES, SCALES, AND DISTANCES  

Topographical maps come in different sizes dependent on the scale utilized to draw the map. The most applicable map for SAR work is the 7.5 min USGS topographical map. The name is derived from the section of the earth that is covered by a map which is 7.5 arc minutes of longitude by 7.5 arc minutes of latitude. The linear distance along the lines of constant longitude remains constant at 7.5 Nautical Miles, NM, (6020 ft/ NM). The horizontal linear distance covered by a map is effected by the latitude of the map section and is therefore always less than 7.5 NM except at the equator. For a map section at 34 degrees latitude ( Southern California ) the horizontal distance across a 7.5 min map would be approximately 6.2 NM. (7.5 X Cosine (Lat or 7.06 start miles)) The next larger scale size, 15 min maps, are also applicable for SAR operations but do not provide the detail that is provided by the 7.5 min maps. Since the 15 min maps cover the same area as four 7.5 min maps, the 15 min maps are applicable to large scale searches in the Sierra back country. Larger scale maps are available but their use in SAR is limited to presentation areas, briefing charts, and downed aircraft searches.  

The map page contains information other than that represented by the map symbols on the actual map. The upper right and lower right hand corners of the map contain the official USGS name for the map quad and the scale of map (i.e. 7.5 min, 15.0 min, etc.). The name of the associated state is included in the name as in " Bear Valley , CA ." The map also contains the names of each of the surrounding map quads of the same scale. In older maps the names are placed along the sides or in the corners of the map closest to the corresponding quad. Newer maps utilize a numbered grid picture with an associated table located along the bottom edge of the map as is shown in figure -1. Above the name in the lower right corner is a legend of any special map symbols that the chartologist noted to be specifically applicable to the map quad. Also in the lower right hand corner is the revision date, and the photo revision date. The revision date is the date of release of a fully updated map with all known features properly noted on the map. Photo revision is an easier and less costly way for the USGS to update the existing map which uses aerial photography and precision avionic equipment to superimpose new chartology onto a map. Photo updated sections of a map are always drawn in purple.

 The center bottom of the map contains the linear distance scale and the contour interval. The contour interval is the vertical elevation distance represented by the contour lines on the map. The lower left hand corner contains a legend that indicates the difference between true, magnetic, and grid North. The left and right map border edges are aligned with true north. Also contained along the edges and in the corners are the Latitude and Longitude for there respective points. Although Lat and Long are cumbersome to localized navigation, the ability to utilize a Lat / Long position given from a military aircraft detecting a downed aircraft is necessary in locating the plane. UTM "grid tick" are markers drawn in light blue along all sides of the map. Grid ID numbers associated with the specific UTM northing and easting coordinates. Township and range numbers for the Public Land Usage System, which is a grid system currently being phased out of the SAR world, are also noted along the border of the map.  

The linear scale of a 15 min map is equivalent to 1 statute mile (5280 ft/mile) per 1 inch on the map. One inch on a 7.5 min map is equivalent to 2000 ft. Another useful conversion for 7.5 min maps is 1 millimeter is approximately equal to 80 ft. The millimeter is often used in localized navigation. Also on a 7.5 min map, 4mm is roughly equivalent to a 100 meter UTM tick.

MAP SYMBOLS  

Map symbols can be categorized into five sections: Man Made which are represented in black (or red to stress major or main), Water Features which have a blue color, Vegetation Symbols which have a green color, Elevation Features which are noted in Brown, and Boundary and Bench Mark symbols which may be red or black.  

Man made structures include: roads, highways, inhabitable buildings, non-inhabital buildings, airports, railroad related features, transmission lines, and pipelines. A color guide to map symbols is available from the USGS mapping service. SAR maintains a stock of these pamphlets. The symbols are reproduced in figure -2 albeit not in color. Often times man-made objects are used as points for triangulation. If man made objects are used, the map should be carefully checked for updates as sections or curves in roads could have been rerouted or moved since the map was created. Also water tanks which are often easy to see at a distance may be a relocated replacement tanks for noted tanks that have collapsed in the past. Items such as large silver mine entrances rarely change over time. For these reasons it is best to use natural (non-man made) objects for position verification.  

It is not necessary to memorize each of the map symbols to be able to utilize a map efficiently. The symbols are selected to make themselves apparent. Knowing the color code of the symbols informs the user of the type of information that is being portrayed. Names and other demarcation (also in black) will also help to identify the symbol to the user.  

MAP PREPARATION FOR FIELD USE  

To facilitate operations with individual maps some map preparation is required after a map is purchased prior to using it in the field. After purchase of a map the user should study the map quickly to note prominent peaks, road availabilities, and any special features. The owner's name should be written in the lower right hand corner of the map. The lower right hand corner is selected as this corner is visible when the map is folded in accordance with the folding instruction given below.  

 

To help in map to compass and compass to map measurements, True N/S Lines should be added to the map using a black ball point pen. The distance between the lines is arbitrary, but 7 or 8 vertical lines across the map page as shown in figure -3 is sufficient. The keep the lines as close to true north south as possible the following procedure should be utilized. Use a long straightedge capable of covering the complete length of the map. A "T" square is optimal. Locate the 8 alignment ticks (black in color located in the areas indicated in figure -4. Align the four on the left and draw a line through them. Then repeat for the right hand set of marks. These lines are now parallel to the left and right edges of the map. Then draw the other lines onto the map by noting the distance to the lines that were drawn first.  

UTM lines should be drawn using a red ball point pen. These lines should connect all the blue UTM tick markers across and "up and down" the page. This will form one kilometer grids throughout the map. UTM northing and easting numbers should be copied onto the map so the N/E values can be read while the map is folded.

Any new local update information should be drawn onto the map. Information concerning new trails, new roads, gate combinations, or hazard areas should be added to the maps. For example the trails noted on the Mugu State Park map should be drawn onto the Newbury Park and the Triunfo Quads. The names of the trails and campsites should also be added. This allows the SAR member in the field to correlate information being passed from someone (an RP) using a park map.  

Since SAR operations often occur in inclement conditions, consider waterproofing the set of maps carried. Two commercially available preparations are available: Stormproof which is a petroleum based sealer and Weatherproof (by REI) which is a polymer coat.  Krylon Crystal Clear which is a spray coating available from art stores reportedly works well and is easy to apply.  

The Stormproof is much easier to apply and leaves the surface of the map more conducive to writing. Weatherproof when applied properly (takes 8 hours to dry) seals the paper in a coating which in theory should keep the map better protected. With either preparation, the maps will be susceptible to moisture at the folds and at any tears. Maps not protected in some manner will become useless to an operation very quickly if exposed to a harsh rain or body sweat. A coated map will last longer over all, but the most important feature of a coated map is that it will be useful in harsh conditions. Another way to protect maps in the field is by using either commercially sold map carriers which are transparent or by keeping the map in a zip lock bag. When using a bag, the map is taken out, folded to present the area of interest and then placed back in the bag for protection. Note that maps should not be stored in the commercially available map cases as the ink from the maps has been known to permanently disfigure the plastic case when stored for long periods (especially in hot places). Any markings to be added to the map should be added to the map prior to coating the maps with any waterproofing material.  

To fold the map in the most useful manner begin by lying the map, face up on a flat surface. Fold the map in half by bringing the top of the map to the bottom and creasing in the center. Then fold the top of the map back to the center line crease and form another crease. Turn the map over and fold the bottom of the map back to the center line crease. A side view of the map at this stage is shown in figure-5. With the map now folded into four sections with the bottom of the map facing upward, fold the map in half from the right side to the left side and crease again. Then fold the right side of the map back to the last crease so the name of the map (actual lower right hand corner of the unfolded map) is facing upward. Turn the map over and fold the left side of the map back to the center line and crease to complete the folding. This allows the maps to be easily carried in a backpack. Some members prefer to turn the map 90 degrees prior to starting the process so that both sides show the map name when folded.

 

TOPOGRAPHICAL LINES AND CONTOUR FORMS  

Contour lines are the means used to represent the three-dimensional ground as a plain view on two-dimensional paper. The vertical height represented between contour lines is called the contour interval, and in mountainous areas is commonly 40 - 80 feet. Every fifth or fourth contour is an index contour shown as a heavier line with a number showing the elevation. Some contour lines actually correspond to real lines on the ground. For example, the shore line of the ocean is a line which represents a particular elevation. This is the sea level contour. Now, imagine the ocean rising 40 feet, creating a new shore line. This would correspond to a contour line 40 feet above the original sea level. Thus, a contour line is an imaginary line on the ground which is always at a constant elevation.

With practice it is possible to visualize the shape of land forms by looking at the pattern of contour lines. To help distinguish ridge lines from gullies and canyons, look for stream drainage patterns which is identified by the blue water patterns. A useful rule to remember is that contours across stream channels and draws are normally V-shaped, and the V's always point upstream (uphill). Contours that cross ridge lines, create V's that face the downhill direction, The direction can be confirmed by noting the elevation numbers on the index contours. Remember that steep slopes are characterized by contour lines very close together. Likewise gentle slopes are characterized by contour lines that are further apart. Figure -6 contain diagrams indicating a contour line representation of a three dimensional objects.  

Landscape features which are prominent are known as control points. The terminology used to describe certain control points is given in figure -7.

   TRAIL PROFILES AND TRAVEL TIMES  

A very powerful tool in the planning of a trip is a trail profile as shown in figure -8. The trail profile indicates the total distance and total elevation gain (and loss) of a given trip. In addition, it can be seen at a glance which legs of the proposed trip will be hard and which will be easy. By combining this information with the time-distance formulas, (20 min per mile plus 30 min per 1000 ft elevation gain), it is possible to calculate the time required to do the trip. In regards to search and rescue, this may indicate if the missing person is in sufficient condition for the trip that has been undertaken,. This could also help the command post in estimating team travel times in the field when extended back country travel is required.  

To create a trail profile, start by marking on the map, starting and ending points, and al points along the proposed line of travel where the slope is changing from ascending to descending or vice versa. Measure the horizontal distance (along the route of travel) between the selected points and plot the distance on a convenient scale. Then plot the above points on any convenient vertical scale at the proper elevation. Add as many intermediate points as are needed to make the plot more representative. Note that the actual slopes plotted are exaggerated unless the vertical and horizontal scale is the same (not recommended). The map section pertaining to the trail profile given is contained in figure -9.

REPORTING POSITION IN THE UTM COORDINATE SYSTEM  

It is very important to know your position continuously during an operation. Whether traveling in an area governed by the public land usage system or not, one member should continually note the team's position on the map. This provides for quick and exact updates when requested by the command post. Incremental navigation is more accurate and easier than attempting to locate a position from scratch each time it is required.  

Universal Transverse Mercader (UTM) is a flat earth mapping scheme popularized by the U.S. Army and various other ground troops. Positions in the field are normally presented as 100 meter grid coordinates. In this case, only a resolution of 100m in Northing/Easting is given. Higher accuracy can be given for special details such as evidence locations when the accurate position is known. The GPS units read to the 1 meter resolution (with varying accuracy - best accuracy 40 meters). In classical UTM presentations, the UTM coordinates are given Northing first followed by Easting. (A variant of UTM called MGRS reverses the position of Northing/Easting. For example, in one meter resolution, 3779000E340000 is a valid location in Agoura just south of the 101 Freeway. The same location listed in 100 meter resolution is N37790E3400. The position is normally abbreviated by giving the least 3 significant digits of each parameter only (as this is adequate for the standard search area). So the same location given above would be given as 790:400.

Be careful when working with other teams out of county. To be clear, one could say North 790, East 400. If transmitting a higher resolution position (especially one from a GPS unit) one should advise "Full 1 meter UTM N37790E3400 - GPS Level 1, 3D", where the "Level 1 3D" is the status being presented by the GPS unit.  

In the lower left hand corner where the magnetic declination is given, the UTM grid North offset is also given. The grid north offset indicates the difference between true North and UTM grid North in the center of the map quad. The variance across a 7.5 min map at AB 34 degree latitude is not great.  

To report one's location, the SAR member should locate the defined value of the kilometer grid in which he is located.  

Map edges are marked with blue tick marks every kilometer in Northing and Easting. A properly formatted map has these tick marks connected to form 1 kilometer UTM grids. The tick marks are normally annotated with the 1 and 10 kilometer digits. Every so often the 100 and 1000 kilometer digits are given for clarity. To locate further resolution, the SAR member must measure. The team supplies members with a small template that facilitates taking this reading. The template is graduated in 100m increments. By placing the "target zero" over the position, one may read the 100 m Northing/Easting by noting the number that lines up the bottom left hand corner. Without the template the SAR member could measure the distance East and North from the bottom left hand corner in millimeters. Dividing the millimeter reading by 4 gives the proper UTM 100 meter digit. At first, this may seem clumsy but with some practice it becomes quite simple and efficient.  

Speak clearly and slowly, giving sufficient time for the receiving party to write down the location information. If possible, transmit the current elevation as an added piece of information to confirm the proper location. Also, if there are other identifiable parameters, such as "On the trail", "at the trail junction," "under the main cliff," or altitude, these should be transmitted along with the exact public land usage coordinates. Never indicate position by giving the estimated distance down a trail or similar qualitative indicators.

REPORTING POSITION WITHOUT USING UTM COORDINATES  

 In the event that the operation is being controlled from a map copy that does not support the markings (which should be rare), report the compass range  (in millimeters) and bearing (True) from a prominent geographic feature or prominent marking on the map of the area to a location on the map. (Do not use a prominent geographical point if it is not on the same map quad as the locating being reported.) For the example given in figure -11, the location would be radioed as follows:

Command post, Rescue 306: 10-20 is from the tip of letter "A" in Moorpark, 92 degrees, out 15 millimeters.

  

Command post, rescue 306: 10-20 is from Peak __, 92 degrees, out 15 millimeters.  

Again, it is helpful to include additional information, such as altitude, near trail junctions, etc., if it is applicable. Also, a team should use the same prominent point for successive location reports to minimize confusion. Also, if there is a possibility of confusion of which map quad is in effect, also transmit the name of the map quad when reporting your location.

HOW A COMPASS FUNCTIONS  

The earth is surrounded by magnetic lines of force which extend from the magnetic north pole located in the north portion of the Hudson Bay, Canada , to the magnetic south pole located in Antarctica . The magnetic needle of the magnetic compass, when held level and allowed to swivel freely, will align itself parallel to the lines of force. The red portion of the compass needle will always point to the magnetic north pole. The angle of declination is the difference between true north and the magnetic north in Hudson Bay . Some compasses such a the Silva Ranger Model 15CL pictured in figure-12 mechanically compensates for the angle of declination to allow the user to read true bearing directly. Compasses that do not mechanically compensate for the angle of declination read magnetic bearing. To convert true bearing to magnetic bearing, simply add the "angle of declination". If on the east coast, the declination is considered to be westerly or positive. If west of Hudson Bay, the declination will be easterly and considered to be negative. See the map of the United States shown in figure-13.  

The actual magnetic declination changes over the period of several years. New declination information is calculated by the government every 10 to 20 year. Also, local anomalies exist which affect the declination in specific areas. Always check the declination specified by the local map for any magnetic anomaly information that may exist in a given area.  

The proper Angle of Declination and the UTM grid North Offset for the center of the map can be found at the bottom left hand corner of USGS topo maps, as is shown in figure-14. The parts of the compass are shown in figure-15.  

 COMPASS ADJUSTMENTS FOR MAGNETIC DECLINATION  

A true bearing to a landmark is the horizontal angle (measured clockwise in degrees) from the true north direction to line of sight from the current position to the landmark. As previously mentioned, compasses are designed to measure "magnetic bearings". A few compasses have a built-in device to compensate for the current declination. The less expensive compasses do not have this but the same results can be accomplished by using the following procedure:

1.   Cut a piece of colored tape the same size and shape as the red orienting arrow in the rotating base plate.  

2.   Set the declination angle on the index of the compass. This angle is determined from the declination diagram in the lower left hand corner of the map.  

3.   Turn the compass over, and place the tape arrow on the underside so that it points right at the index. (Figure -16). 

4.   Check for the proper placement of the tape arrow in the following way. Place the compass directly over the declination diagram on the map so that the magnetic needle pivot point on the compass is over the apex of the declination diagram and the red orienting arrow on the base plate lines up with true North on the declination diagram. If the tape arrow is placed properly, it should exactly align with the magnetic North line on the declination diagram.

MEASURING TRUE BEARING WITH A COMPASS IN THE FIELD  

Bearings are taken in the field from present positions to known landmarks to allow triangulation to locate an exact location on a map. A bearing may also be needed if a destination or route chosen from a map and one would like to verify that he is still on the chosen route. Field compass bearings are often required to keep a line search progressing properly through a densely wooded area.  

To begin taking a compass bearing in the field, hold the compass in one hand close to the chest in a level position so the needle can swivel freely. The direction of the travel arrow on the base plate should be pointing straight ahead from the user. Compasses that have a sighting mirror may be used for added accuracy when aligning to an object. Keep the position of the compass and the body fixed, rotate the whole body to face the landmark of interest. With one hand, turn the central dial until the orienting arrow (or tape arrow) is exactly underneath the red (north) part of the magnetic needle. If a sighting mirror is not being used, be sure to look directly down on the compass needle from above and make this alignment exactly. If a sighting mirror is being used, hold the compass at eye level and view the compass dial in the mirror. Accuracy of bearing measurements is much more dependent on this visual alignment than any other element. The true bearing to the land form is now set into the compass and can be read on the index. With a little practice, one should be able to consistently take a bearing usually within 2 degrees accuracy in less than 10 seconds. Be careful that jewelry, pens, watches, or other objects do not distort the measurement. Stay away from power lines, machinery, and operating vehicles.  

Orientation of the Map in the Field  

To orient a map means to place it in a manner that the features presented on the map align themselves with the landmarks on the ground. This can be accomplished in two ways. Orientation of the map by inspection is the preferred method because it is fast, but not accurate. Orientation of the map using the compass is used when great accuracy is desired, or when inspection is confusing.

 To orient by inspection, locate several prominent landmarks and compare them to their relative position on the map. This should help in locating some of the less prominent landmarks as a check of the orientation. The top of the map should then be in the northerly direction.  

To orient to a compass heading of true north, first set the compass to read true north (0 degrees in a compensated compass). Then align a red line in the rotating baseplate along a true North-South line on the map (edge of map, meridian line, true North line). Be sure the red orienting arrow in the rotating baseplate points north on the map (not south). With the map held flat, rotate map and compass together until the north magnetic needle is over the orienting arrow. The map is now oriented to true north.

More Maps (Direction)

 

  
Ventura County Sheriff's Volunteer Search & Rescue  |  Fillmore Mountain Rescue  |  Team 1
Mailing Address:  P.O. Box 296 |  Fillmore, CA  93016
 
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2005 Ventura County Sheriff's Volunteer Search & Rescue, Fillmore Mountain Rescue, Team 1

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