Question: What is a map?
Answer: A topographic map is a mathmatically determined presentation of a portion of the earth's surface. Manmade and natural features are depicted by symbols, lines, colors, and forms.
Question: Why are maps important?
Answer: A map provides comprehensive information on the existance and location of, and the distances between, ground features such as populated places, routes of travel and communications, and extent of vegetation cover. It also indicates varations in land forms and heights of natural features
1: Componets of a map.
These are what is included on a topographic map.
A: Marginal Information
Before useing any piece of equipment. One should always read the instruction for that piece of equipment. This is also true with maps. The instructions are placed around the outer edges of the map and are known as marginal information. All mapsare not the same so it becomes necessary, every time a different map is used.To examine the marginal information carefully.
1. Sheet Name; The sheet name is found in two places. The center of the upper margin and the right side of the lower margin. Generally, a map is named after it's outstanding cultural or geographic feature. When ever possible the name of the largest city on the map is used.
2. Sheet Number; The sheet number is found in the upper right margin and is used as a reference number for that map sheet.
3. Series Name and Scale; The map series name is found in the upper left margin. A map series usually comprises of a group of similar maps at the same scale and on the same shhet lines or format designed to cover a particular geographic area. It may also be a group of maps to serve a common purpose, such as the military city maps
The scale note is a representative fraction which gives the ratio of a map distance to the corresponding distance on the earth's surface. For example, the scale note 1;50,000 indicates that one unit of measure on the map equals 50,000 units of the same measure on the ground.
4. Series Number; The series number appears in the upper right margin and lower left margin. It is a comprehensive reference expressed either as a four digit numeral, or as a letter, followed by a three or four digit numeral.
5. Edition Number The edition number is found in the upper margin and in the lower left margin. It represents the age of the map in relation to other editions of the same map and the agency resonsible for its production. The latest edition will have the highest number.
6. Bar Scales; The bar scales are located in the center of the lower margin. They are rulers used to convert map distance to ground distance. Maps have three or more bar scales, each in a different unit of measure.
7. Credit Note; The credit note is in the lower left margin. It lists the producer, dates, and general methods of preparation or revision. This information is important to the map user in evaluating the reliability of the map as it indicates when and how the map information was obtained
8. Adjoining Sheets Diagram; Maps at all standard scales contain a diagram which illustraits the adjoining map sheets.
9. Index to Boundaries; The index to boundaries diagram appears in the lower or right margin of all sheets 1:100,000 scale or larger, and 1:1,000,000 scale. This diagram, which is a miniature of the map area, shows the boundarieswhich occur within the map area, such as county lines and state boundaries. On 1:250,000 scale maps, the boundary information is included in the Location Diagram.
10. Projection Note; The projection system is the framework of the map. For military maps, this framework is the confromal type, ie, small areas of the surface of the earth retain their true shapes on the projection; Measured angles closely approximate true values; and the scale factor is the same in all directions from a point. The projection is identified on the map by a note in the lower margin.
11.Grid Note; The grid note in the center of the lower margin. It gives information pertaining to the grid system used, the interval of the grid lines, and the number of digits omitted from the grid values. Notes pertaining to everlapping or secondary grids are also included when appropiate.
12. Grid Reference Box; The grid reference box contains instructions for composeing a grid reference.
13. Vertical Datum Note; This note is located in the center of the lower margin. It designates the basis for all vertical control stations, contours and elevations appearing on the map.
14. Horizontal Datum Note; This note is located on the center of the lower margin. It indicates the basis for all horizontal control stations appearing on the map. The network of these stations controls the horizontal positions of all mapped features.
15. Legend; The legend is located in the lower left margin. It illustrates and identifies the topographic symbols used to depict some of the more prominent features on the map. The symbols are not always the same on every map. To avoid error in the interpretation of symbols the legend must always be referenced to when a map is read.
16. Declination Diagram; The declination diagram is located in the lower margin of large scale maps dn indicates the angular relationships of true north, grid north, and magnetic north. On maps at 1:250,000 scale, this information is expressed as a note in the lower margin.
17. Users Note; A users note is located in the center of the lower margin. It requests cooperation in correcting errors or omissions on the map. Errors should be marked adn the map forwarded to the agency identified in the note.
18. Unit Imprint; The unit imprint, located in the lower right margin, identifies the agency which printed the map and the printing date. The printing date should not be used to determine when the map information was obtained.
19. Control Interval; The control interval note appears in the center of the lower margin. It states the interval distance between adjacent contour lines on the map. When supplementary contours are used, the interval indicated.
20. Special Notes and Scales; Under certain coditions, special notes or scales maybe added to the marginal informationto aid the map user. The following are examples:
a. Glossary; A glossary is an explanation of technical terms or a translation of terms on maps of forien area where the native language is other than english.
b. Classifification; Certain maps require a note indicateing the security classification. This is shown in the upper an dlower margins.
c. Protractor Scale; A protractor scale may appear in the upper margin on some maps. It is used to lay out the magnetic grid declination for the map which in turn is used to orient the map with the aid of a magnetic compass.
d. Coverage Diagram; Onmaps at scales of 1:100,000 and larger, a coverage diagram may be used. It is normally in thelower or right margin and indicates the methods by which the map was made, dates of photography, and reliability of the sources. On maps at 1:250,000 scale, the coverage diagram is replaced by a reliability diagram.
e. Elevation Diagram; On some maps at scales of 1:100,000 an dlarger, a miniature characterization of the terrain is shown by a diagram in the lower tight margin of the map. The terrain is represented by a band of elevation, spot elevations, and major drainage features. The elevation guide provides the map reader with a means of rapid recogination of major land forms.
f. Special Notes; A special note is any statement of general information that relates specifically to the mapped area.
21. Stock Number Identification; All maps published by and for theCorps of Engineers which are in the Department of the Army (Defense?) supply system, contain stock number identifications, which are used in requistioning map supplies. the identification consists of the words "STOCK NO." followed by a unique designation which is composed of the series number, the sheet number of the individual map and on recently printed sheets, the edition number.
2. Topographic Map Symbols and Colors
This is what is on a map.
A. The purpose of a map is to permit one to visualize an area of the earth's surface with pertinent features properly positioned. Ideally, all the features within an area would appear on th emap in their true porportion, position, and shape. The map maker has been forced ot use symbols to represent the natural and manmade features of the earth's surface. These symbols resemble, as closely as possible, the actual features themselves but as though viewed from above
B. To facilitate the identification on the map by providing a more natural appearance and a contrast, the topographic symbols are usually printed in different colors, with each color identifying a class of features. The colors vary with different maps, but on a standard large-scale topographic map, the colors used and the features each represent are:
1. Black; The majority of cultural or manmade features
2. Blue; Water features such as lakes, rivers, and swamps.
3. Green; Vegetation such as woods, orchards, and vineyards
4. Brown; All relief features such as contours.
5. Red; Main roads, built up areas, and special features.
6. Occasionally other colors may be used to show special information. These, as a rule, are indicated in the marginal information
3. Terrain Features
What are different terrain features? Name them.
How do you identify terrain features on a map?
1. A knowledge of map symbols, grids, scale, and distance gives one enough information to identify two points, locate them , measure between them. A map user must also become proficient in recognizing the various landforms and irregularities of the earth's surface and be able to determine the elevation and differences in height of all terrain features.
a. Datum Plane; This is a reference from which vertical measurements are taken. The datum plane for most maps is mean or average sea level.
b. Elevation; This is defined as the height (vertical distance) of an object above or below a datum plane. c. Relief; Relief is the representation of landforms and the characterization of the earth's surface.
2. The elevation of points and the relief of an area affect the movement and deployment of unitsby limiting the route along which they may travel, their speed of movement, and the ease or difficulty of attacking of defending an area. Also affected are observation, fields of fire, cover, concealment, and the selection of key terrain features.
B. Contour Lines:
1.There are several ways of indicating elevation and relief on maps. The most commonway is by contour lines. A contour line is aline representing an imaginary line on the ground along which all points are at the same elevation.
Contour lines indicate a vertical distance above or below a datum plane. Starting at sea level, normally the zero counter, each contour line represents an elevation above sea level. The vertical distance between adjacent contour lines is known as the contour interval and the amount of the contour interval is given in the marginal information. Every fifth contour line is drawn with a heavier line. These are known as index contours and someplace alongeach index contour the line is broken and its elevation is given. The contour lines falling between index contours are called intermediate contours.They are drawn with a finer line than the index contours and usually do not have their elevations given.
2. Using the contourlineson a map, the elevation of any point may be determined by:
a. Finding the contour intervalof the mapa from the marginal information, and noting both the amount and the unit of measure.
b. Finding the numbered contour line (or other given elevation) nearest the point for which the elevation is being sought.
c. Determining the direction of slope from the numbered contour line to the desired point.
d. Counting the number of contour lines that must be crossed to go from the numbered line to the desired point and noting direction-up or down. The number of linescrosseddmultipliedby the contour intervalis the distance above or below the starting value.
Note: For values between the contour lines use the following. From the line to 1/4 of the distance to the next line it is concidered to be the same elevation as the contour line. From 1/4 to 3/4 the distance between the contour lines use 1/2 the value of the contour interval. For 3/4 to the nesxt contour line it is the value of that contour line.
C. Terain Features
In order to show the relationship of land formations to each other and how they would be symbolized on a contour map, styleized panoramic scetdhes of the major relief formations were drawn and a contour map of each sketdh was developed.
1. Hills; A point or small area of high ground. When you are located on a hilltop, the ground slopes down in all directions. A hilltop is indicated on a map by a fully enclosed circle.
2. Valleys; A stream course which has at least a limited extent of reasonably level ground bordered on the sides by higher ground. The valley generally has manouver room within its confines. Contours indicating a Valley are U-shaped and tend to parallel a major stream before crossing it. The more gradual the fall of a stream, the farther each contour parallels it. The curve of the contour always point up stream.
3. Draw; A less developed stream course in which there is essentially little or no manuever room with in its confines. The ground slopes upward on each side and towards the head of the draw. Draws occur frequently along the sides of ridges, at right angles to the valley between them. Contours indicating a draw are V-shaped, with the point of the "V" toward the head of the draw.
4. Ridge; A line of high ground, with normally minor variations along its crest. The ridge is not simply a line of hills; all points of the ridge crest are appreciably higher than the ground on both sides of the ridge.
5.Spur; A usually short, continuously sloping line of higher normally jutting out from the side of a ridge. A spur is often formed by two roughly parallel streams cutting draws down the side of the ridge.
6. Saddle; A dip or low point along the crest of a ridge. A saddle is not necessarily the lower ground between two hilltops; it may be simply a dip or break along an otherwise level ridge crest.
7. Depression; A low point or sinkhole, surrounded on all sides by higher ground.
8. Cuts and Fills; Man-made features by which the bed of a road or railroad is graded or leveled off by cutting through high areas and filling in the low areas along the right of way.
9. Cliff; A vertical or near vertical slope. When a slope is so steep that it cannot be shown at the contour interval without the contours coalescing, it is shown by a ticked "carrying" contour or contours, The ticks always point toward lower ground.
4. Use of Map, Compass, and Protractor
A. Direction Finding
1. Base Lines; In order to measure anything there must always be a starting point or zero measurement. To express a direction as a unit of angular measure there must be a starting point or zero measure and a point of reference. These two point designate the base or reference line. There are three base lines, true north, magnetic north, and grid north. The most commonly used are magnetic north and grid north; the magnetic when working with a compass, and the grid when working with a map.
a. True North; A line from any position on the earth's surface to the north pole. All line of longitude are true nort lines. True north is usually symbolized by a star.
b. Magnetic North; The direction to the north magnetic pole, as indicated by the north seeking needle of a magnetic instrument. Magnetic north is usually symbolized by a half arrowhead.
c. Grid North; The north that is established by the vertical grid lines on the map. Grid north may be symbolized by the letters GN or y.
2. Azimuth and Back Azimuth; The most common military method of expressing a direction is by using azimuths. An azimuth is defined as a horizontal angle, measured in a clockwise manner from a base north line. When the azimuth between two points on a map is sesired, the points are joined by a straight line and a protractor is used to measure the angle between grid north and the drawn line. This measured line is the grid azimuth of the drawn line. Azimuths take their name from the base line from which they have been measured; true azimuths from true north, magnetic azimuths from magnetic north, and grid azimuths from grid north. So there are three ways to express an azimuth.
a. Back Azimuth; A back azimuth is the reverse direction of an azimuth. It is comparable to doing an "about face". To obtain a back azimuth froma an azimuth, add 180 degrees if the azimuth is 180 degrees or less, or subtract 180 degrees if the azimuth is 180 degrees or more. The back azimuth of 180 degrees may be stated as either 0 degrees or 360 degrees.
3. Declination Diagram; A declination diagram is placed on most large scale maps to enable the user to orient the map propperly. The diagram shows the interrelationship of magnetic north, grid north, and true north. On medium scale maps declination information is shown by a note in the map margin.
a. Declination is the angular difference between true north and either magnetic north or grid north. There are two declinations, a magnetic declination and a grid declination.
b.The declination diagram contains three prongs representing the three norths.
(1). G-M Angle; An arc, indicated by a dashed line, connects the grid north and the magnetic north prongs. The value of this arc-the grid-magnetic angle (G-M Angle) states the size of the angle between grid north and magnetic north ane the year it was prepared. this value is expressed to the nearest 1/2 degree with mil equivalents shown to the nearest 10 mils.
(2).Grid Convergence; An arc, indicared by a dashed line, connectsthe prongs for true north and grid north. The value of the angle for the center of the of the sheet is given to the nearest full minute with its equivalent to the nearest mil.
(3). Conversion Notes; Notes may also appear in conjunction with the diagram explaining the use of the G-M angle
(4). It is often necessary to convert from one type of direction to another. A magnetic compass reading fives a magnetic azimuth, but to plot this line on a gridded map, the magnetic azimuth must be changed to a grid azimuth. The reverse is true when orientation is taken from a the map; the grid azimuth measured from the map must be converted to a magnetic azimuth for use with a magnetic compass. The declination diagram is used for these conversions.
4. The Compass and Its Uses; The magnetic compass is the most commonly used and simplest instrument for measuring directions and angles in the field. The compass we will discuss is the lensatic compass.
a. The lensatic compass must always be held level and firm when sighting on a objective and reading an azimuth. There are several techniques for holding the compass and sighting.
(1). With one method, the slit in the eyepiece, the hairline front sight in the cover, and the target are alined. The azimuth can then be read by glancing down at the dial through the eyepiece. This technique provides a reading precise enough to use for resection and intersection.
(2). To use the second method, open the cover until it forms a straight edge with the base, pull the eyepiece to the rear-most position.(GI type compasses only). Next, place your thumb through the thumb loop, form a steady base with your third and fourth fingers and extend your index finger along the side of the compass. Place the thumb of your other hand between the eyepiece and the lens; extend the index finger along the remaining side of the compass and the remaining fingers around the fingers of the other hand, pull your elbows firmly into your sides. This will place the compass between your chin and belt. To measure an azimuth, simply turn your entire body toward the object, pointing the compass cover directly at the object. Once you are pointing at the object , just look down and read the azimuth from beneath the fixed black index line.
b. For night use, special features of thecompass are the luminous markings and the 3 degree bezel serration and clicking device. Turning the bezel ring to the left causes an increase in azimuth while turning it to the right causes a decrease.
One method for determining compass directions at night follows:
(1). Rotate the bezel until the luminous line is over the black index line.
(2). Hold the compass with the left hand and rotate the bezel ring with the right hand, in a counterclockwise direction, to the number of clicks required. The number of clicks is determined by dividing the value of the required azimuth by three.
(3). Turn the compass until the north arrow is directly under the luminous line on the bezel.
(4). Hold the compass open and level in the palm of the left hand with the thumb along the flat side of the compass. In this manner, the compass can be held consistently in the same position. Position the compass approximately halfway between between the chin and belt, pointing to your direct front. A little practice in daylight will make you proficient in pointing the compass the same way every time. Looking directly down into the compass, turn body until the north arrow is under the luminous line. Then proceed in the direction of the front of the compass
c. Certain precautions regarding the care and use of a compass.
(1). Handle with care, the dial is set at a delicare balance which a shock could damage.
(2). Always keep the compass in its protective container when not in use. Kep it put away when not is use, but is should be readily avalible when needed.
(3). When the compass is to be used in total darkness, an initial azimuth should be set, if possible, while light is still avalible. With this initial azimuth as a base, any other azimuth which is a multiple of three degrees can beestablished through the clicking feature of the bezel.
(4). Compass readings should never be taken near visible masses of iron or electrical circuits. The following are suggested as approximate safe distances to insure propper functioning of the compass.
High tension power lines....................55m
Field gun, truck, tank.........................18m
Communications wires,barbed wire......10m
Helmet or rifle....................................0.5m
5. Orientation of a Map
Before a map can be used it must be oriented. A map is oriented when it is in a horizontal position with its north and south corresponding coresponding to north and south on the ground.
A. A simple way to orient a map is with a compass.
(1). With the map in a horizontal position, the compass is placed parallel t othe north-south grid line with the cover side of the compas (forward end) pointing toward the top of the map
(2). Rotate the map and compass until the directions of the declination diagram formed by the black index line and the compass needle match the directions shown on the declination diagram printed on the margin of the map. the map is then oriented.
(3). If the magnetic north arrow on the map is to the left of grid north, the compass reading will be equal to the G-M angle (given in the declination diagram). If the magnetic north is to the right of grid north, the compass reading will equal 360 degrees minus the G-M angle.
Protractors come in several forms-full circle, half circle, square, and rectangular. All of them divide a circle into units of angular measure, and regardless of their shape, consist of a scale around the outer edge and an index mark. The index mark is the center of the protractor circle from which all the direction line radiate.
A. to determine the gid azimuth of a line form one point to another on the map.
(1). Draw a line connecting the two points.
(2). Place the index point of the protracter at the point where the line crosses a vertical (north-south) grid line.
(3). Keeping the index at this point, aline the 0 degree-180 degree line of the protractor on the vertical grid line.
(4). Read the value of the angle form the scale; this is the grid azimuth of the point.
B. To plot a direction line from a known point on a map.
(1). Convert, if necessary, the direction to a grid azimuth.
(2). Construct a north-south grid line through the known point:
a. Approximately aline the 0 degree-180 degree line of the protractor in a north-south direction through the known point.
b. Holding the 0-180 degreeline of the protractor on the known point, slide the protractor in the north-south direction until the horizontal line of the protractor (connecting the protractor index and the 90 degree tick mark) is alined an an east-west grid line.
c.Draw a line connecting 0 degree, the known point, and 180 degree.
(3). Holding the 0-180 degree line coincident with thisline, slide the protractor index to the known point.
(4). Make a mark on the map at the required angle.
(5). Draw a line from the known point through the mark made on the map. this is the grid direction.
The location of an unknown point by successively occluping at least two but preferably three known positions and sighting on the unknonwn point is called intersection. It is to locate features that are not defined on the map or which are not readily identifiable. There are two methods of intersection. The only method we will explore is the map and compass method.
A. Map and Compass Method
(1). Orient the map using the compass.
(2). Locate an dmark your position on the map.
(3). Measure the magnetic azimuth to the unknown position; convert to grid azimuth.
(4). Draw a line on the map from your position on this grid azimuth.
(5). Move another position or have another team in a different location complete steps one through four one more time.
(6). To check accuracy complete one more time steps one through five.
(7). Where the line cross is the location of the unknown position. Using three lines a triangle is sometimes formed instead of an intersection. this is called the triangle of error. if the triangle is large recheck your work to find the error. do not assume the the position is in the center of the triangle.
The location of the user's unknown position by sighting on two or three known features is called resection. Resection can be done with or with out a compass. We will only explore the map and compass method.
A. Map and Compass Method
(1). Orient the map using the compass.
(2). Locate two or three known positions on the ground and mark them on the map.
(3). Measure the magnetic azimuth to a known position: convert to grid azimuth.
(4). Change the grid azimuth to a back azimuth and draw a line on the map from the known position back toward your unknown position.
(5). Repeat steps one through four, for the second back azimuth.
(6). Repeat steps one through four, for a third back azimuth.
9. Position Location by One Line
A. Location of a distant point by one line: Often it is not possible or practicable to occupy two positions to preform intersection. Direction can be used to assist location from one position only.
(1). Determine the one line of direction from your position to the distant point.
(2). Draw that line of direction on the map.
(3). Inspect the terrain in the vicinty of the distant point for distinctive terrain features.
(4). Inspect the map along the line of direction to find those same features. Estimation of range should assist in such ground-map comparison. Plot the map position of the point on the line of direction according to the pattern of terrain features you have observed.
(5). Plot the map position of the point on the line of direction according to the pattern of terrain features you have observed
(6). Although sometimes not practical, this technique often results in a reasonably accurate determination of direction.
B. Location of User's Position by One Line: The same technique described in section "A" can often be used to locate your own position. The principal difference is that you must change the azimuth to a back azimuth, since you are drawing the line on the map from the distant point back through your own position.
10. Grid Coordinate Scale
A. Grid Coordinate Scale; A grid coordinate scale divides a grid square more accurately than can be done by estimation, and the results are more consistent. Also this scale has been designed for the express purpose of plotting grid coordinates. The grid coordinate scales are located on military protractors (GTA 5-2-12 1981)
(1). The 1:25,000/ 1:250,000 scale (lower left corner of the protractor) subdivides the 1,000m grid block into 10 major subdivisions, each equal to 100 meters. Each 100m block has five graduations, each equal to 20m. Points falling between the two graduations can be read accurately to 10m, this value being the fouth and eigth digits of the coordination.
(2). The 1:50,000 scale (upper right on the protractor) subdivides the 1,000m grid block into 10 major sudivisions each equal to 100m. each 100m block is then divided in half. Points falling between these graduations must be estimated to the nearest 10m for the fourth and eighth digits of the coordinates.
(3). The 1:100,000 scale (lower left corner of the protractor) subdivides the 1,000m grid block into 8 major subdivisions each equal to 200m. Each 200m block is then divided in half. Points falling between these graduations msut be estimated to the nearest 50m for the fourth and eighth digits of the grid coordinates.
(4). To use the coordinate scale for the determinnation of coordinates, place the scale with the zeros of the scale at the lower left corner of the grid square. Keeping the scale on the lower horizontal grid line, slide it to the right until the point for which coordinates are desired touches the edge of the scale. When reading coordinates, examine the two sides of the coordinate scale to insure that the horizontal scale is aligned with the east-west grid line, and the vertical scale is parallel with the north-south grid line.
B. Point Designation; The designation of a point is based on the military priciple: read RIGHT then UP. The precision desired determines the number of digits to be read beyond the principal digits. It should be impressed upon the students that the term grid coordinate often includes both the 100,000m square identification and the desired number of digits. In many instances it is a tactical requirement that the 100,000m square identifier be included in any point designation.
(1). Reading RIGHT-UP, coordinates XXXX locate the 1,000m grid square in which point "z" is located.
(2).To locate the point to the nearest 100m, estimates the tenths of the gridsquare from grid line to point, in the same order (RIGHT-UP). Give complete coordinate RIGHT, then complete coordinate UP.
(3)The precision of a point reference is shown by the number of digits in the coordinates-the more digits, the more precise the location.
a. A four digit - XXXX = a 1,000m grid square
b. A six digit - XXxXXx = to the nearest 100m
c. A eight digit - XXxaXXxa = to the nearest 10m
d. A ten digit - XXxabXXxab = to the nearest meter
(4). If a scale is not avalible that exactly divides the side of the grid in tenths or hundredths, these divisions may be made by slanting the the scale until it fits the interval between grid lines.
(5). Coordinates are written as one continous number without spaces, parentheses, dashes, or decimal points. From this it should be obvious that whoever is to use the written coordinates must know where to make the split between the RIGHT reading and the UP reading; for this reason, the coordinates of the point within the 100,000m square must always contain an even number of digits.
11. Grid Zone Identifiers
In the military map system there are many different zones. So the Dept. of Defense has a systm of identifiying each map sheet within a grid zone.
a. Grid zone; This is based on a longitude and latitude reference. This is expresed as a two digit number.
b. Grid Zone Designation; this further indicates a point with in a certain grid zone. This is expresed as a letter after the two digit number.
c. 100,000m Square Identification; The addition of two more letters further locates a point within a 100,000m grid square. In military grid coordinates this two letter identifier is used when giving a military grid coordinate. The grid identifier is located in the marginal information.
U.S. Army FM 21-26 Jan 69