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Measurement and construction (determination) of distances on a topographic map

Измерения и построения на топографической карте

Map Scales

Измерения и построения на топографической карте
Fig. 1. Designing numerical and linear scales on topographic maps and city plans

The map scale shows how many times the length of a line on a map is less than the corresponding length on the ground. It is expressed as a ratio of two numbers. For example, a scale of 1:50 000 means that all terrain lines are depicted on the map with a decrease of 50,000 times, i.e. 1 cm on the map corresponds to 50,000 cm (or 500 m) on the terrain.

The scale is indicated under the bottom side of the map frame in numerical terms (numerical scale) and as a straight line (linear scale), on the segments of which the corresponding distances on the ground are signed (Fig. 1). The scale value is also indicated here - the distance in meters (or kilometers) on the ground, corresponding to one centimeter on the map.

It is useful to remember the rule: if you cross out the last two zeroes on the right side of the relationship, the remaining number will show how many meters in the terrain corresponds to 1 cm on the map, i.e. the magnitude of the scale.

When comparing several scales, the one with the number on the right side of the relation is smaller. Suppose that for the same piece of terrain there are maps of 1: 25000, 1: 50,000 and 1: 100,000 scales. Of these, a scale of 1: 25,000 will be the largest, and a scale of 1: 100,000 will be the smallest.

The larger the scale of the map, the more detail it shows the terrain. With a decrease in the scale of the map, the number of terrain details applied to it decreases.

The detail of a terrain image on topographic maps depends on its nature: the less parts the terrain contains, the more fully they are displayed on maps of smaller scales.

In our country and many other countries, the main scales of topographic maps are: 1: 10,000, 1: 25,000, 1: 50,000, 1: 100,000, 1: 200,000, 1: 500,000 and 1: 1,000,000.

The maps used in the troops are divided into large-scale, medium-scale and small-scale.

Measurement on the map of straight and winding lines

Map scale

Card Name

Card classification

by scale

according to the main purpose

1:10 000 (in 1 cm 100 m)

ten thousandth

large scale

tactical

1:25 000 (in 1 cm 250 m)

twenty thousandth

1:50 000 (in 1 cm 500 m)

five thousandth

1: 100,000 (in 1 cm 1 km)

one hundred thousandth

medium scale

1: 200,000 (in 1 cm 2 km)

two hundred thousandth

operational

1: 500,000 (in 1 cm 5 km)

five hundred thousandth

small scale

1: 1 000000 (in 1 cm 10 km)

millionth

Measurement on the map of straight and winding lines

When measuring straight lines, the compass needle is placed on the end points, then, without changing the compass solution, the distance is taken along a linear or transverse scale. In the case when the compass solution exceeds the length of the linear or transverse scale, a certain integer number of kilometers is determined by the squares of the kilometer grid, and the remainder is determined by the usual order of the linear or transverse scale.

It is convenient to measure broken lines by successively increasing the compass solution with straight-line segments. The distance corresponding to the compass solution is determined by the order outlined above.

Measurement of distances along curves is made by compass pitch. The length of the compass pitch depends on the degree of tortuosity of the line, but, as a rule, it should not exceed (for accurate measurements) 1 cm. To eliminate errors due to deformation of the paper (map), the compass pitch length is preliminarily checked along the kilometer grid line. To measure the distances on the map using an odometer, turn the dial to the zero (initial) division, then roll the wheel with uniform pressure from the starting point to the end point. At the same time, it is necessary to pay attention to the fact that when advancing the curvimeter, the readings of the counting of the path increase, and not decrease; otherwise, the odometer must be rotated 180 °. If the scale of the odometer is signed in kilometers, the resulting distance is read directly from the scale.

If the scale of the odometer is signed in kilometers, the resulting distance is read directly from the scale. If the scale divisions are given in centimeters of the wheel's track on the map, then the resulting number of divisions must be multiplied by the division price. In order to avoid an error, the price of division is recommended to be determined by reference measurement along the kilometer grid line.

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When measuring straight lines, the compass needles are set at the end points, then, without changing the compass solution, the distance is taken along a linear or transverse scale:

  • Determination of distances on a linear scale using a compass In the case when the solution of a compass exceeds the length of a linear or transverse scale, a certain integer number of kilometers is determined by the squares of the kilometer grid, and the remainder by the usual order of the linear or transverse scale. It is convenient to measure broken lines by successively increasing the compass solution with straight-line segments.
  • Measurement of distances by the method of building up a compass solution The distance corresponding to a compass solution is determined by the order outlined above. Measurement of distances along curves is made by compass pitch. The length of the compass pitch depends on the degree of tortuosity of the line, but, as a rule, should not exceed (for accurate measurements) 1 cm. To eliminate errors due to deformation of the paper (map), the compass pitch length is preliminarily checked along the kilometer grid line.

To determine the distance between points of a terrain (objects, objects) using a numerical scale, you must measure the distance between these points in centimeters on a map and multiply the resulting number by the magnitude of the scale.

For example, on a 1: 25000 scale map, measure the distance between the bridge and the windmill with a ruler (Fig. 2); it is equal to 7.3 cm, multiply 250 m by 7.3 and get the desired distance; it is equal to 1825 meters (250x7.3 = 1825).

Измерения и построения на топографической карте
Fig. 2. Determine the distance between the points of the terrain using the ruler.

A small distance between two points in a straight line is easier to determine using a linear scale (Fig. 3). To do this, a compass meter is enough, the solution of which is equal to the distance between the specified points on the map, attach to the linear scale and take a reading in meters or kilometers. In fig. 3 The measured distance is 1070 m.

Измерения и построения на топографической карте
Fig. 3. Measurement on the map with a linear compass gauge.
Измерения и построения на топографической карте
Fig. 4. Measurement on the map by the caliper gauge along twisting lines.

Large distances between points along straight lines are usually measured with a long ruler or caliper.

In the first case, the numerical scale is used to determine the distance on the map using a ruler (see Fig. 2).

In the second case, the “step” of the compass gauge is set so that it corresponds to an integer number of kilometers, and an integer number of “steps” is laid on the segment measured on the map. The distance that does not fit into an integer number of "steps" of the compass meter is determined using a linear scale and added to the resulting number of kilometers.

In the same way, measure distances along winding lines (Fig. 4). In this case, the “pitch” of the measuring caliper should be taken 0.5 or 1 cm, depending on the length and degree of tortuosity of the measured line.

Измерения и построения на топографической карте
Fig. 5. Distance measurement with a odometer

To determine the length of the route on the map, a special device, called an odometer (Fig. 5), is used, which is especially convenient for measuring winding and long lines.

The device has a wheel, which is connected by a gear system with an arrow.

Измерения и построения на топографической карте

When measuring the distance with the odometer, you need to set its arrow on division 99. Holding the odometer in a vertical position, guide it along the measured line, without tearing it from the map along the route so that the scale readings increase. Bringing to the end point, count the measured distance and multiply it by the denominator of the numerical scale. (In this example, 34x25000 = 850000, or 8500 m).

Accuracy of measuring distances on the map. Corrections for the distance for the slope and tortuosity of lines

The accuracy of determining distances on the map depends on the scale of the map, the nature of the measured lines (straight, winding), the chosen method of measurement, the terrain, and other factors. Most accurately determine the distance on the map can be in a straight line.

When measuring distances using a compass gauge or a ruler with millimeter divisions, the average measurement error in flat terrain usually does not exceed 0.7–1 mm at the map scale, which is 17.5–25 m for a 1: 25000 scale map, the scale is 1: 50000 - 35-50 m, the scale is 1: 100000 - 70-100 m.

In mountainous areas with a large steepness of slopes, errors will be greater. This is explained by the fact that when taking pictures of a terrain, the length of the projections of these lines on the plane, rather than the length of lines on the surface of the Earth, is plotted on the map.

For example, With a slope of 20 ° (Fig. 6) and a distance of 2120 m on the ground, its projection onto a plane (distance on the map) is 2000 m, i.e., 120 m less. It is estimated that with a slope angle (slope steepness) of 20 °, the resulting measurement of the distance on the map should be increased by 6% (6 meters added by 100 m), by 15% for a slope of 30 °, and by 23 for an angle of 40 ° %

Измерения и построения на топографической карте
Fig. 6. The projection of the length of the slope on the plane (map)

When determining the length of the route on the map, one should take into account that the distances along the roads, measured on the map with the help of a compass or an odometer, in most cases are shorter than the actual distances.

This is explained not only by the descents and ascents on the roads, but also by a certain generalization of the convolutions of the roads on the maps. Therefore, the result of measuring the length of a route derived from the map should be multiplied by a factor indicated in the table, taking into account the nature of the terrain and the scale of the map.

The simplest ways to measure areas on the map

Terrain

The ratio of the increase in the length of the route, measured on a map of scale

1: 50,000

1: 100,000

1: 200,000

Mountain (rugged)

1.15

1.20

1.25

Hilly (midland)

1.05

1.10

1.15

Plain (slightly intersected)

1.00

1.00

1.05

Approximate assessment of the size of the area produced by eye squares kilometer grid, available on the map. Each square of the grid of maps of scales 1: 10000 - 1: 50000 on the terrain corresponds to 1 km2, to the square of the grid of maps of scale 1: 100,000 - 4 km2, to the square of the grid of maps of scale 1: 200000 - 16 km2.

More precisely, areas are measured with a palette, which is a sheet of transparent plastic coated with a grid of squares with a side of 10 mm (depending on the scale of the map and the required measurement accuracy).

Putting such a palette on the measured object on the map, firstly calculate the number of squares that fit completely inside the contour of the object, and then the number of squares intersected by the contour of the object. Each of the incomplete squares is taken as half a square. As a result of multiplying the area of ​​one square by the sum of squares, the area of ​​the object is obtained.

According to squares of 1: 25000 and 1: 50,000 squares of small areas, it is convenient to measure with an officer's ruler having special rectangular cutouts. The areas of these rectangles (in hectares) are indicated on the ruler for each scale of the scale.

Determination of distances by rectangular coordinates

The distance D along a straight line between points with known rectangular coordinates, given in one system, can be most accurately determined by the formula:

D=V(Х2-Х1)2+(Y2-Y1)2

Where:

  • X1, Y1 - coordinates of the starting point;
  • X2, Y2 - coordinates of the end point.