Obtaining necessary for the card should be good to study it: set the year compilation and publication of maps; familiarize itself with the conventional signs, know the magnetic declination, which is usually imposed for frame maps, determine the scope, determine the cross section of the relief, explore scale congestion and allocate greater visibility area of interest with colored pencils: forest — green, water — blue, roads — brown, bridges and causeway — black, various landmarks — red, etc.
Numerical and graphical scale maps are usually placed below the map, under the frame. If for some reason there is no scale on the map and you must determine if you can use one of the following methods.
Defining the scope of the nomenclature list
Depending on the location map sheet letters and numbers that make up its range of different, but the order and number them in the nomenclature of this scale is always the same.
Scaling along parts of the meridian
It is known that in the middle latitudes of the USSR arc length 1 ° meridian is 111.1 km (104 mile), and the arc length of 1'' is about 1855 m (869 fathoms). In the framework card signed by their latitude (parallels) and longitude (meridians), and large-scale maps are broken down into minutes.
To determine the scale of the map, measured in centimeters (or inches) long segment of a meridian between the parallels, or the length of one of its minutes. Assume that the measured distance of 1.8 cm were found to be on the same card, and 5 inches on a different map. Hence the scale of these maps are calculated as follows:
1) 1855 m: 1.8 = 1855 Ltd.: 18 = 103 055 cm = 1030 m;
2) 52 mile: 5 = 10.4 miles.
Due to inaccuracies in the measurement allowed a compass and perhaps some deformation maps here, approximate value scale. Since the cards are issued at a given scale, it is easy to guess that the first map has a scale of 1: 100 000, ie, a 1-cm 1 km, and the second card — desyativerstka — 10 miles to 1 inch.
Scoping for grid
Measure the distance between the lines of the grid and define but indicated number (for example, on the western frame — 28, 30, 32, 34, or on the southern frame — 06, 08, 10), how many miles they are carried out. This determines the scale of the map. Clearly, the lines are drawn after 2 km.
Distance on the map between adjacent lines is 2 cm, therefore, 2 cm on the map correspond to 2 km on the ground. The map scale is 1: 100 000.
Defining the scope of the distance between local objects
If the map shows the two objects, such as kilometer posts along the road, the distance between them on the ground is known, to determine the scale to the number of meters between the objects on the ground divided by the number of inches between them on the map.
Example. The distance between adjacent kilometer posts on the map is 2 cm, on the ground — 1000 m Therefore, the map scale of 1: 50 000, or 1 cm card equivalent to 500 m on the ground.
Defining the scope of the other cards on the map to zoom in on known
Comparing the measured distance between two identical points on both cards and knowing the scale of one of them, determine the scale on the other.
Example. On the map, the scale of which is not known, the distance between points is 6.5 cm same distance measured on the map, the scale of which is known, is 3 km 250 m This card will be determined by the scale of 3 km 250 m: 6.5 cm = 50 Ltd. cm, or 1 cm 500 m
Defining the scope of a direct measurement of the distance on the ground
When none of the previous methods are not suitable for some reason, and we are in the area shown on the map with an unknown scale, we choose a more or less equal to the area two objects lying close to each other, and the distance between them on the ground in steps and on the map in centimeters.
Example. Kilometer posts on the road to the silo about 400 steps, or 300 m, as one step is 75 cm on the map between the same objects measured 3 cm Hence the scale of our map 300: 3 = 100 m to 1 cm, or 1 10 000.
Determination of the contour interval
Typically, the cross section contour is put over a linear scale, or under it. If the inscription is missing, determine the height of the cross section contour can be on their marks, or marks on the points.
To determine the height of the cross section on the difference between the marks contours have two adjacent markers adjacent contour lines that express the same slope (for example, 60-50 = 10), divided by the number of spaces between the horizontal lines (5). Quotient of (10: 5 = 2) will give in meters or fathoms vertical interval for the map sheet. In this case, it is 2 pm
To determine the height of the cross section contour points by marks should Height difference of two points (eg, 54,1-42,7 = 11.4) divided by the difference between the number of periods (4-2 = 2) from the nearest point to the contour lines common to both horizontal dots (D). Quotient of (11,4:2 = 5.7) is usually not whole numbers, and numbers rounded to multiples of 5, 10, 20, with metric measures, or to numbers that are multiples of 2 and 4 in the old Russian measures. From this section height contours for the card 5 m
Cross-section contours depends on the scale and the nature of the survey the terrain, for example:
where h — the distance between the horizontal planes intersecting relief.
Nasal scale and determining the slope of ramps
Each card has its own scale foundation, upon which the steepness of slopes. At the inception of the field can be found by the edge of the paper. It is applied to the place on the map, the slope is to be determined, and dashes mark the distance between adjacent contour lines. The paper was then applied to the scale of the pledged so that one dash coincided with the base, and the other — with a curve of the scale, and then read at the base value of steepness. In our case, the slope of the road is 1 ° (Fig. 35).
For an approximate determination of the steepness of slope, you can use the following rule: the number of times the inception of less than 1 cm, as many times the steepness of slope greater than 1 °.
To determine the steepness of slope on the ground, to get up the side of the ramp, take two equal sticks and putting them at eye level (one horizontal, which should correspond to lay the ramp, and the other vertical, which should correspond to its height), to estimate how many times the height of the slope is less than its inception.
Example. Suppose the height of the slope is less than its inception in 4 times. Define the steepness of slope in degrees. To do this, 60 * to divide that number by 4. The steepness of a slope of 15 °.
The eye to estimate the steepness of the slope can be with the fingers (Fig. 36).