The right tick mark (b) is aligned with the 3,000-meter mark in the primary scale, thus the distance is at least 3,000 meters. To convert the map distance to ground distance, move the paper down to the graphic bar scale, and align the right tick mark (b) with a printed number in the primary scale so that the left tick mark (a) is in the extension scale ( Figure 5-4).įigure 5-4. Transferring map distance to paper strip.ī. Make a tick mark on the edge of the paper at each point ( Figure 5-3).įigure 5-3. To determine straight-line distance between two points on a map, lay a straight-edged piece of paper on the map so that the edge of the paper touches both points and extends past them. ![]() When using the graphic scale, be sure to use the correct scale for the unit of measure desired.Ī. Most maps have three or more graphic scales, each using a different unit of measure ( Figure 5-2). To the left of the zero, the scale is divided into tenths and is called the extension scale. To the right of the zero, the scale is marked in full units of measure and is called the primary scale. The graphic scale is divided into two parts. GRAPHIC (BAR) SCALESĪ graphic scale is a ruler printed on the map and is used to convert distances on the map to actual ground distances. As the scale becomes smaller, the accuracy of measurement decreases because some of the features on the map must be exaggerated so that they may be readily identified. When determining ground distance from a map, the scale of the map affects the accuracy. 044 meters x 100 (centimeters per meter)Į. Occasionally it may be necessary to determine map distance from a known ground distance and the RF: MD (c) Using the GD and the MD from the first map, determine the RF using the formula: RFĭ. Using the RF for this map, determine GD, which is the same for both maps. ![]() ![]() (b) Locate those same two points on the map that have the known RF. (a) Select two points on the map with the unknown RF. (2) Comparison With Another Map of the Same Area that Has an RF. (d) Both the MD and the GD must be in the same unit of measure and the MD must be reduced to 1. (c) Use the RF formula and remember that RF must be in the general form: RF (b) Determine the horizontal distance between these same two points on the ground-ground distance (GD). (a) Measure the distance between two points on the map-map distance (MD). To be able to determine ground distance on such a map, the RF must be determined. The situation may arise when a map or sketch has no RF or scale. In the metric system, the standard unit of measurement is the meter.ġ00 meters is a regular football field plus 10 meters.Īppendix C contains the conversion tables.Ĭ. Since the distance on most maps is marked in meters and the RF is expressed in this unit of measurement in most cases, a brief description of the metric system is needed. The map distance from point A to point B is 5 unitsĥ x 50,000 = 250,000 units of ground distanceī. Converting map distance to ground distance. The ground distance between two points is determined by measuring between the same two points on the map and then multiplying the map measurement by the denominator of the RF or scale ( Figure 5-1).įigure 5-1. ) An RF of 1/50,000 or 1:50,000 means that one unit of measure on the map is equal to 50,000 units of the same measure on the ground.Ī. (It could be yards, meters, inches, and so forth. The RF is always written with the map distance as 1 and is independent of any unit of measure. This scale is usually written as a fraction and is called the representative fraction. The numerical scale of a map indicates the relationship of distance measured on a map and the corresponding distance on the ground. The ability to determine distance on a map, as well as on the earth's surface, is an important factor in planning and executing military missions. ![]() The scale of the map permits the user to convert distance on the map to distance on the ground or vice versa. CHAPTER 5 SCALE AND DISTANCE A map is a scaled graphic representation of a portion of the earth's surface.
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