§ 7. Working with topographical maps
1. Remember that device helps to target areas.
2. What is azimuth?
3. What ways You can measure distances on the map?
People love rest of nature, making a trip unfamiliar areas. By help you can appeal to experienced travelers or travel agencies, and can try the same route to develop such a trip. This can be useful topographical map. It can pave the optimal pre- travel route and reached the selected area to navigate it. Guided by a map means: the parties to define the horizon, to discern it and local relief items to set your location and path transportation.
Defining areas. Navigate topographic map quite easily, if locality is more or less open (plain, not occupied by buildings or woods) and has enough facilities-orientation. However, in woods, mountains or in poor visibility verify the card with the terrain is difficult, and sometimes impossible. Then perform the movement in azimuth - the direction angle, which initially measured on the map protractor, and the area determined by using a compass.
However, a map and compass measure different azimuth. By defining topographic map fiysnyy azimuth- Angle between geographic north (true) meridian and the direction of certain point. His vidlichuyut the course clockwise. At the same location compass determine mz – angle between the north magnetic meridian and direction at a certain point. He counted the progress clockwise. Magnetized compass needle is directed along magnetic meridian and blue tip pointing to the north magnetic pole, which does not match the geographic North Pole. Thus, the magnetic meridian by its direction does not coincide with the actual form of the meridians and their angles.
The angle between the northern directions and actual magnetic meridian is called magnetic Instigating (δ). It must be considered when moving from the actual azimuth to magnetic. Declination is the East, if the direction of magnetic north meridian east deviates from the true meridian northerly direction, and Western - if it deviates to the west of true north direction meridian. To go to the actual azimuth (A) a magnetic (Am) should: if declination east, then subtract its value from true azimuth, and if west - add to the actual azimuth, ie Am = A?
Topographical map makes it possible to determine the azimuth angles. Y-kut - a angle between the north vertical line kilometer grid and direction on point. Him and true azimuth, protractor measure the progress clockwise from 0 to 360 °. To switch from the azimuth angle to mz, take into account the angle between the north vertical line kilometer grid and magnetic meridian. This angle called adjusted toward, or aberration arrow. Rejection is east, if the magnetic north direction arrow deviates east of kilometer vertical lines, and Western, if the needle deviates to the west.
To calculate mz (Ам) amendments have value direction (П) at the eastern deviation subtracted from the value grid angle (£) And in western – add to the value of the azimuth angle: Am = £ ± П.
Value magnetic declination and amendments in the direction of different points of the globe unequal. These figures indicate a special schematic drawings that located on the topographic map at its southern border.
Fig. Correlation between magnetic and true azimuth and the azimuth angle
Fig. Formation of magnetic angle declination (δ)
Measurement distances. Using topographic maps can be fairly accurately calculate the distance to area. Straight segments between two points on a topographic map measured ruler compasses. If you do not have them handy, you can use strip of paper, making it into points. Distance withdrawn from the maps or compasses reflected on a paper strip, can be translated into real using linear scale, placed under the lower frame map. Length broken lines (eg roads, railways) are calculated as the sum of segments direct.
Difficult measure the length of the winding lines - rivers, coastlines, forest paths etc.. You already know that in such cases, you can use floss, making it into a curve so that its shape again. For more precise measurements using instrument for measuring curves - odometer. He consists of a rolling wheel and the dial with an arrow that shows traveled map distance in centimeters on the ground or in kilometers.
Determination elevation. Relief on topographic maps depicted contoured - section lines ruggedness horizontal plane conducted at regular intervals in height. Distance (in meters) between January neighboring planes is called section height. Difference heights of neighboring contour lines is also height section. Height of section relief on the map indicated in linear scale.
Horizontal conducted a continuous brown line. All points that lie on one horizontally, have the same absolute height, as indicated on individual horizontally. It differs from the height of horizontally adjacent points on vi. Knowing this, we set the absolute height anywhere that is not necessarily marked on the horizontal. Except , the absolute height subscribed to separate horizontally at the tops of some mountains and hills, and near certain objects, such as branching roads, wells and springs. The shoreline of rivers, ponds, lakes are given mark water edge, that show the absolute height of the water surface at a given point.
All horizontal, lockable within map sheets, indicate or raise (Mountain or hill), or fall (hollows) in relief. To distinguish these forms relief as know the direction their slopes can be digital signatures Horizontal and notes some height, by location of reservoirs and for berhshtryhamy. During the campaign it is important know the relative heights of different points of terrain, steepness of slopes etc.. This You can find the number and density contour lines held on topographic map: the more contour lines on a slope, so it is higher: the horizontally held close to each other, so it is cooler, the longer - the more sloping.
Am = A - δ = 54° 00' – 6° 30' = 47° 30'
Fig. Determination actual azimuth and the azimuth angle for topographic map and transfer them to magnetic azimuth
Fig. Picture contoured hill
(Height 5 m sections)
Fig. Sheet Topographic maps
Identify areas on topographic map and locality using azimuth: azimuth valid - the angle between the northern geographical area (true) meridian and direction to a point; mz – angle between magnetic north meridian and direction at a certain point.
The transition the actual magnetic azimuth to be taken into account magnetic declination - angle between the northern areas of true and magnetic meridians.
Gb - is the angle measured on topographic map between north vertical kilometer mesh and direction to a point.
Relief is portrayed on the map contoured – lines of horizontal cross-sectional area of inequalities planes carried out at regular intervals in height. Distance between January neighboring planes is called a high cross section.
Questions and Tasks
1. For topographic map and identify geographical rectangular coordinates Andozka Mountain, located in square 6611.
2. Protractor measure the actual azimuth and the azimuth angle direction d. Andozka (square 6611) - G. Tsegel'na (square 6613). Click on these values a magnetic azimuth of this direction.
3. Define the absolute height of the point where the forester house (square 6611).
4. Measure the distance from the railway station to the central city Snov Part of the village along the highway and Kim dirt road. In which part of the road observed the largest slope angle?
Practical work 2
Using conventional symbols and scale Topographic maps and applying in paragraph techniques with her can be quite detailed description of an area displayed on the map. Describe the area under the plan.
1. Location of land: that is populated outskirts item displayed, geographic coordinates of the item.
2. Рelyef surface: flat (flat, hilly) or mountain area, its overall shape, the highest and lowest absolute height individual elements of relief and their characteristics.
3. Inland water area: rivers and their tributaries, the direction flow, the presence of lakes, reservoirs, ponds, swamps, springs.
4. Natural vegetation: forests, their location, species composition, shrubs, individual trees and meadows.
5. List and location of commercial, agricultural and socio-cultural objects.
6. Traffic: main road, their destination.