Measuring distances
What is distance?
Distance is the space between two places. Distances may be long or they may be short. Whatever the distance we always use a fixed measure, which is usually meters in our case. Smaller distance is measured in centimeters and longer distances in kilometers.
You can have maps of a small village, a large country, a continent or even the world. But the map of a country in your atlas will not show you all the details of the village found in the map of a small village, just as the map of your locality did not show you all the details of your office that you find in the map plan of your office.
This is called the scale line. Every map in your atlas a scale line so that you can calculate the distance from one place to another. Find the map of India in your atlas. Measure the distance from Delhi to Mumbai with a piece of thread. Hold this thread against the scale line to find the distance in kilometers from Delhi to Mumbai.
A scale is a ratio by which the distance between any two points on the map is compared with the distance covered on the ground.
What is direction?
Direction is taken from the word direct, that is, to show the way. If we want to reach our destination we must travel in the proper direction. We are familiar with the four directions of north, south, east and west. These as you know, are further divided into north-east, north-west, south-east and south-west.
From the illustration of the compass you will see that these can be further broken down again into even smaller divisions such as NNE (north, north -east), ENE “(east north-east), ESE, SSE, SSW, WSW, WNW and NNW. Thus we have the sixteen points of the compass.
How do find the directions?
1) On a bright day it is easy to find the east, as the sun rises in the east and sets in the west. If we stand with our right hand to the east, then we face the north and our back is to the south.
2) Suppose you get lost while traveling on a bright, cloudless night. You could find your directions by looking for the pole or North Star. Looking first for a group of stars known as the plough or big Dipper and follow an imaginary line from the two rights –hand stars in the plough. This line leads to a bright star, all by itself. This is the North Star.
3) If you are traveling by car and your car broke down, you would want to find out exactly where you are. With a good road map and a mariner’s compass you could easily tell the direction in which you are traveling. How can you do this?
The compass has a magnetic needle which is balanced at its centre on a pivot. This enables the needle to swing freely on a dial on which the cardinal points are marked. When the compass is placed on a flat surface, the needle will swing from side to side and will finally come to rest. It will always point in the same direction indicating the north and south magnetic poles. The shaded or the colored half of the needle indicates the north.
In order to know the direction in which you are traveling, you have to turn the compass around till the pint marked N on the dial comes under there north of the needle. Now you can find your directions by looking at the other letters on the compass. S, E and W point to the south, east and west respectively. This is called setting the compass.
The compass was called the Mariner’s compass because mariners or seaman used it to find the direction over the oceans.
Bearings
Today people find it easier and more accurate to divide the compass into the 360 degrees of a circle. This means due east is 90 degrees due south is 180 degrees and due west is 270 degrees.
Survey maps
Traveling to new and unknowing places can be fun and exciting but it would be wise to set out with a map to guide us if we wish to explore an area really will. For this we particularly require survey maps.
Maps are accurate representations of a part, or sometimes the whole of the earth on a flat sheet of paper. Maps which represent the hills and valleys, the coasts, the railways, the roads, the bridges, the towns, the monuments and such features on an area in great detail are called survey maps.
These features are represented by special symbols, signs and colors which are known as conventional symbols. These symbols are explained on the map, for example, black lines denote railway while blue lines denote rivers. Roads are normally shown by colored lines but the color and thickness very with the type of road shown.
So you can find maps that show only the area you want to travel in, or the part of the country you want to see. A survey map can tell you things like the location of the station, the rest house, the post office, the hospital, the police station.
The scale of the map also gives you important information because there is definite relationship between the size of the map on paper and the size of the area on the ground. One centimeter on the map could mean one kilometer on the ground. So you can measure the exact distance that you have to travel to reach certain place.
Survey maps also use several methods to show the relief of general layout of a place. This is called the topography.
Contour lines are lines which connect all places which are of the same height above the average level of the sea. The average level of the surface of the sea is given on maps as the mean sea level. Sometimes spot heights are given, so that you know the exact height of, say, a mountain peak. Areas of the same height are often shaded or colored the same to tell you the photography.
Modern maps are highly accurate and their mapping requires expensive and complex equipment for measuring distance and angles. Telescope instruments called theodloites are used. Today, more and more land details are being mapped by the faster method of aerial photography.
Survey maps differ from other maps because they give us the detailed topography of an area.
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