Basic calculations of distance and area on the maps
DISTANCE ON THE MAP
One may be asked to calculate or measure the distance of a river; road, railway, electric transmission line etc on the map. It should be noted that some of theses distances may be straight while others may bne winding.
Measurement of straight line distances on the map.
To measure a straight line on the map, a pair of dividers or a straight edge of paper are the best instruments to be used. To measure two points on the map on a straight line, the two points must be identified first, using grid reference values. Open or stretch out the arms of the pair of dividers to fall exactly on the two points along the straight line, or if it is the edge of paper, it should be placed along the straight line to cover the two points A - B and then marked out on the paper. After opening the pairs of dividers or making the two points on the edge of paper, these two are taken and placed along a graduated ruler to get the reading in centimeters. This reading in centimeters is not the ground didtance and so must be converted to actual ground distance which is always in kilometers.
Measurement of a winding distance or course
To measure a winding distance an a map, a string or thread and paper edge can be used.
- MEASURING WITH A PIECE OF PAPER
Using a sharp pencil, candidates have to divide the road, river, railway, footpath or electricity transmission line to be measure in to sections which are fairly straight. They can now place the straight edge of the piece of paper along the different portions or sections of the line until they come to the end of the point of the rooad or river they are to measure.
This length can noow be taken and measured against a graduated ruler which is, the after converted into ground distance.
NB: Note should be taken that the formulae for conversion remains the same for all the methods of measurements. But the map scale changes accoording to each map.
2. MEASURING WITH A STRING OR THREAD
Candidates have to identify the distance to be measured and mark them out. They can now go ahead to use the string or thread to follow the curve and bends carefully till the end. The point at the end of the thread or string has to be marked off and then the string or thread taken off from the map. The distance measured is then put against graduated ruler in order to obtain the distance in centimeters before converting to kilometers.
Candidates are often asked to calculate the area occupied by a lake, sea, woodland etc. This can easily be measured by the use of some methods. Measurement of areas involve the regular and irregular shapes. The various methods in measuring area include;
Among the above methods, the square method is the most common and widely used. If we are asked to calculate the area of any feature shown on the map using the square methods, the following steps should be considered.
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