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measure distance. Some charts carry a linear scale in the margin, and, where present, it indicates that the
same scale may be used anywhere on the chart.
114 AFPAM11-216 1 MARCH 2001
Figure 4.2. Typical Plotter.
Figure 4.3. Measuring True Course.
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Figure 4.4. Measuring True Course Near 180o or 360o.
4.5.2. Plotting Positions. On most Mercator charts, the spacing between meridians and parallels is
widely spaced, necessitating the use of dividers. There are several methods by which positions can be
plotted on Mercator charts. One method is illustrated in Figure 4.5. Place the straight edge of the plotter
in a vertical position at the desired longitude. Set the dividers to the desired number of minutes of
latitude. Hold one point against the straight edge on the parallel of latitude corresponding to the whole
degree of latitude given. Let the other point also rest against the straight edge and lightly prick the chart.
This marks the desired position. In measuring the latitude and longitude of a position already plotted,
reverse the procedure.
4.5.3. Plotting and Measuring Courses:
4.5.3.1. Step 1—Plot departure and destination on the chart as shown in Figure 4.6.
4.5.3.2. Step 2—Draw the course line between the two points. If they are close together, the straight
edge of the plotter can be used. If they are far apart, two plotters can be used together or a longer straight
edge can be used. If none of these methods is adequate, fold the edge of the charts so that the fold
connects the departure and destination points, and make a series of pencil marks along the edge. A
plotter or straight edge can then be used to connect the points where the chart is unfolded. After the
course line has been plotted, the next step is to determine its direction.
116 AFPAM11-216 1 MARCH 2001
Figure 4.5. Plotting Positions on a Mercator.
Figure 4.6. Reading Direction of a Course Line.
4.5.3.3. Step 3—Place the points of the dividers or a pencil anywhere along the line to be measured.
4.5.34. Step 4—Place the plotter against the dividers.
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4.5.3.5. Step 5—Slide the plotter until the center hole is over the midmeridian. Make a mental estimate
of the approximate direction to avoid obtaining a reciprocal course.
4.5.3.6. Step 6—Read TC on the protractor at the meridian. Using the midmeridian will give an average
TC for the leg.
4.5.4. Plotting Course From Given Position. A course from a given position can be plotted quickly in
the following manner: Place the point of a pencil on the position and slide the plotter along this point,
rotating it as necessary, until the center hole and the figure on the protractor representing the desired
direction are lined up with the same meridian. Hold the plotter in place and draw the line along the
straight edge (Figure 4.7).
Figure 4.7. Plotting Course From Given Position.
4.5.5. Measuring Distance. One of the disadvantages of the Mercator chart is the lack of a constant
scale. If the two points between which the distance is to be measured are approximately in a north-south
direction and the total distance between them can be spanned, the distance can be measured on the
latitude scale opposite the midpoint. However, the total distance between any two points that do not lie
approximately north or south of each other should not be spanned unless the distance is short.
4.5.5.1. In the measurement of long distances, select a midlatitude lying approximately halfway between
the latitudes of the two points. By using dividers set to a convenient, reasonably short distance, such as
60 NM picked off at the midlatitude scale, you may determine an approximate distance by marking off
units along the line to be measured, as shown in Figure 4.8.
118 AFPAM11-216 1 MARCH 2001
Figure 4.8. Midlatitude Scale.
4.5.5.2. The scale at the midlatitude is accurate enough if the course line does not cover more than 5o of
latitude (somewhat less in high latitudes). If the course line exceeds this amount or if it crosses the
equator, divide it into two or more legs and measure the length of each leg with the scale of its own
midlatitude.
4.6. Plotting Procedures for Lambert Conformal and Gnomonic Charts:
4.6.1. Plotting Positions. On a Lambert conformal chart the meridians are not parallel as on a Mercator
chart. Therefore, plotting a position by the method described under Mercator charts may not be accurate.
On small scale charts or where there is marked convergence, the plotter should intersect two graduated
parallels of latitude at the desired longitude rather than parallel to the meridian. Then, mark off the
desired latitude with your dividers. On a large scale chart, the meridians are so nearly parallel that this
　
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