FM 3-25.26 MAP READING AND LAND NAVIGATION

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CHAPTER 4GRIDSThis chapter covers how to determine and report positions on the ground in terms of their locations on amap. Knowing where you are (position fixing) and being able to communicate that knowledge is crucialto successful land navigation as well as to the effective employment of direct and indirect fire, tactical airsupport, and medical evacuation. It is essential for valid target acquisition; accurate reporting of NBCcontamination and various danger areas; and obtaining emergency resupply. Few factors contribute asmuch to the survivability of troops and equipment and to the successful accomplishment of a mission asalways knowing where you are. The chapter includes explanations of geographical coordinates,Universal Transverse Mercator grids, the military grid reference system, and the use of grid coordinates.4-1. REFERENCE SYSTEMIn a city, it is quite simple to find a location; the streets are named and the buildings have numbers. The only thingneeded is the address. However, finding locations in undeveloped areas or in unfamiliar parts of the world can be aproblem. To cope with this problem, a uniform and precise system of referencing has been developed.4-2. GEOGRAPHIC COORDINATESOne of the oldest systematic methods of location is based upon the geographic coordinate system. By drawing a set ofeast-west rings around the globe (parallel to the equator), and a set of north-south rings crossing the equator at rightangles and converging at the poles, a network of reference lines is formed from which any point on the earth's surfacecan be located.a. The distance of a point north or south of the equator is known as its latitude. The rings around the earthparallel to the equator are called parallels of latitude or simply parallels. Lines of latitude run east-west butnorth-south distances are measured between them.b. A second set of rings around the globe at right angles to lines of latitude and passing through the poles isknown as meridians of longitude or simply meridians. One meridian is designated as the prime meridian. Theprime meridian of the system we use runs through Greenwich, England and is known as the Greenwichmeridian. The distance east or west of a prime meridian to a point is known as its longitude. Lines of longitude(meridians) run north-south but east-west distances are measured between them (Figures 4-1 and 4-2).Figure 4-1. Prime meridian and equator.
Figure 4-2. Reference lines.c. Geographic coordinates are expressed in angular measurement. Each circle is divided into 360 degrees, eachdegree into 60 minutes, and each minute into 60 seconds. The degree is symbolized by ° , the minute by ′, andthe second by ″. Starting with 0° at the equator, the parallels of latitude are numbered to 90° both north andsouth. The extremities are the north pole at 90° north latitude and the south pole at 90° south latitude. Latitudecan have the same numerical value north or south of the equator, so the direction N or S must always be given.Starting with 0° at the prime meridian, longitude is measured both east and west around the world. Lines east ofthe prime meridian are numbered to 180° and identified as east longitude; lines west of the prime meridian arenumbered to 180° and identified as west longitude. The direction E or W must always be given. The linedirectly opposite the prime meridian, 180° , may be referred to as either east or west longitude. The values ofgeographic coordinates, being in units of angular measure, will mean more if they are compared with units ofmeasure with which we are more familiar. At any point on the earth, the ground distance covered by one degreeof latitude is about 111 kilometers (69 miles); one second is equal to about 30 meters (100 feet). The grounddistance covered by one degree of longitude at the equator is also about 111 kilometers, but decreases as onemoves north or south, until it becomes zero at the poles. For example, one second of longitude represents about30 meters (100 feet) at the equator; but at the latitude of Washington, DC, one second of longitude is about 24meters (78 feet). Latitude and longitude are illustrated in Figure 4-3.Figure 4-3. Latitude and longitude.d. Geographic coordinates appear on all standard military maps; on some they may be the only method oflocating and referencing a specific point. The four lines that enclose the body of the map (neatlines) are latitudeand longitude lines. Their values are given in degrees and minutes at each of the four corners. On a portion ofthe Columbus map (Figure 4-4), the figures 32° 15' and 84° 45' appear at the lower right corner. The bottom lineof this map is latitude 32° 15'00″N, and the line running up the right side is longitude 84° 45'00"W. In additionto the latitude and longitude given for the four corners, there are, at regularly spaced intervals along the sides ofthe map, small tick marks extending into the body of the map. Each of these tick marks is identified by itslatitude or longitude value. Near the top of the right side of the map is a tick mark and the number 20'. The fullvalue for this tick marks is 32° 20'00" of latitude. At one-third and two-thirds of the distance across the mapfrom the 20' tick mark will be found a cross tick mark (grid squares 0379 and 9679) and at the far side another20' tick mark. By connecting the tick marks and crosses with straight lines, a 32° 20'00" line of latitude can beadded to the map. This procedure is also used to locate the 32° 25'00" line of latitude. For lines of longitude, the
Page 1 and 2: *FM 3-25.26 (FM 21-26)Field ManualN
Page 3 and 4: Chapter7OVERLAYSPurposeMap OverlayA
Page 5 and 6: AAppendixBMAP FOLDING TECHNIQUESApp
Page 7 and 8: PART ONEMAP READINGCHAPTER 1TRAININ
Page 9 and 10: CHAPTER 2MAPSCartography is the art
Page 11 and 12: mission may depend on that map. All
Page 13 and 14: Figure 2-2. Joint operations graphi
Page 15 and 16: 2-8. STANDARDS OF ACCURACYAccuracy
Page 17 and 18: ectangle that represents the sheet
Page 19 and 20: Figure 3-1. Topographical map.3-2.
Page 21: shown in brown, rivers and lakes in
Page 25 and 26: Figure 4-4. Determining latitude.(6
Page 27 and 28: Figure 4-6. Determining geographic
Page 29 and 30: • 5,125 x 300 = 1,537,500• 1,53
Page 31 and 32: Figure 4-9. False eastings and nort
Page 33 and 34: (1) Grid Lines. The regularly space
Page 35 and 36: Figure 4-14. Coordinate scales.(a)
Page 37 and 38: Figure 4-16. Placing a coordinate s
Page 39 and 40: locations. With practice, this can
Page 41 and 42: g. 10-Meter Identification. The gri
Page 43 and 44: south to north. To designate any on
Page 45 and 46: c. The situation may arise when a m
Page 47 and 48: Figure 5-3. Transferring map distan
Page 49 and 50: Figure 5-5. Measuring a curved line
Page 51 and 52: Figure 5-7. Reading the extension s
Page 53 and 54: about 30 inches long. To accurately
Page 55 and 56: Factors AffectingRange EstimationTh
Page 57 and 58: Figure 6-1. Three norths.b. Magneti
Page 59 and 60: Figure 6-4. Measuring an azimuth.WA
Page 61 and 62: . When using the protractor, the ba
Page 63 and 64: azimuth to grid azimuth; the other,
Page 65 and 66: azimuth (Figure 6-12).Figure 6-12.
Page 67 and 68: Intersection is the location of an
Page 69 and 70: Figure 6-18. Resection with map and
Page 71 and 72: Figure 6-20. Modified resection.6-1
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(2) If you have observed any topogr
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(6) Map Reference. Reference is mad
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(3) The shape of the ground area co
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Figure 8-4. Low oblique photograph.
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Figure 8-7. Relationship of cameras
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8-5. SCALE DETERMINATIONBefore a ph
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square or rectangle. After the four
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. If no map is available, the shado
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Figure 8-17. Constructing a point d
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Figure 8-19. Locating the grid coor
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Figure 8-21. Side lap.b. The requir
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Figure 8-24. Placement of stereosco
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(2) Encasing the floating dial is a
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c. Presetting a Compass and Followi
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9-5. FIELD-EXPEDIENT METHODSFigure
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this, make a shadow clock and set y
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9-6. GLOBAL POSITIONING SYSTEMFigur
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CHAPTER 10ELEVATION AND RELIEFThe e
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contour line numbered 600. Locate p
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Figure 10-7. Uniform, steep slope.c
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Figure 10-11. Contour line around a
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Figure 10-15. Gradient.10-6. TERRAI
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Figure 10-19. Valley.(4) Ridge. A r
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Figure 10-24A. Cliff.Figure 10-24B.
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(3) To the south lies a valley; the
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Figure 10-28. Connecting points.(2)
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Figure 10-31. Drawing a hasty profi
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Figure 11-1. Map oriented with 11 d
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Figure 11-4. Map oriented with 10 d
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The key to success in land navigati
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(3) To The South. The terrain gentl
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concealment from enemy observation.
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compare the evidence you encounter
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(10) Because no one can move along
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ecommended. The point man is in fro
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Figure 12-1. Tracked vehicle capabi
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c. Use Terrain Features as Checkpoi
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(7) The distance factor in dead rec
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Table 13-1. Major desert regions.(1
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Mountains are generally understood
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Figure 13-3. Jungles and savannas.a
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trafficability, a deep accumulation
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CHAPTER 14UNIT SUSTAINMENTLand navi
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This sequence can be used to develo
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c. Area Sketches. These sketches in
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Figure B-2. How to slit and fold a
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1 degree = 1/360 circle = about 17.
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APPENDIX DJOINT OPERATIONS GRAPHICS
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APPENDIX FORIENTEERINGWhat is orien
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Figure F-2. A cross-country oriente
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(usually at one-minute intervals) t
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Figure F-5. Recorder's sheet.g. Eve
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F-8. CONTROL POINT GUIDELINESWhen t
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Figure F-9. Map symbols (continued)
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F-10. ORIENTEERING TECHNIQUESFigure
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APPENDIX GM2 COMPASSThe M2 compass
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APPENDIX HADDITIONAL AIDSThis appen
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H-6. GROUND-VEHICULAR LASER LOCATOR
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Step 3. Look at the composition. To
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J-5. COMPATABILITYAll GPS receivers
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• Signal intelligence.• Electro
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Figure K-4. Setup the units.d. The
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Figure K--10. Enter a way point.c.
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Figure K--14. Azimuth.d. The third
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GSRGTAG/VLLDground surveillance rad
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VNASvehicular navigation aids syste
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FM 3-25.26 (FM 21-26)20 JULY 2001By
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FM 3-25.26 MAP READING AND LAND NAVIGATION

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