There are three common types of map scales;
i.
small,
ii.
medium and
iii.
large scale maps.
Small scale maps
a)
On a small-scale map the
degree of reduction is much less and the ratio will be a smaller number.
b)
In East Africa, small
scale maps are drawn to the scale of 1:1,000,000, 1:500,000, 1:250,000,
1:50,000.
Medium scale maps
— Are drawn at 1:25,000, 1:10,000 and 1:2500.
Important point to note
a.
If a linear scale is
doubled, areas will be quadrupled.
b.
It follows that a map on
a scale of 1:100,000 can show four times as much country as one on the same
sheet of paper at 1:50,000.
c.
The type of the scale
therefore determines the size of the map or the distance on the map and the
true distance on the earth’s surface.
Assignment
— Why is the denominator of a small-scale map larger
than that of a large-scale map?
Measurement of Distance along a Road or River
You need to follow the following procedure:
i.
Divide the required
route by light pencil marks into portions that are nearly straight.
ii.
The next thing you
should do is to measure carefully each of these sections with dividers or the
edge of a piece of paper and note down the measurements.
iii.
Add the lengths of
various sections together and measure the total length on the linear scale.
Measurement of Areas
Areas can be
regular or irregular in shape. It is very simple to find their areas.
Regular Shapes
These are in form of
a.
rectangles,
b.
squares or
c.
Rectangles.
For a four-sized figure,
a.
The area is found by
multiplying the width times length.
b.
This implies that you
first measure the lengths.
The area of a triangle
i.
The area of a triangular
shape is found by
ii.
first measuring the
length of the base of the triangle, then
iii.
measure the length of
the perpendicular (height) from the base to the apex.
iv.
The area is half the
first measurement multiplied by the second. (0.5 x base x height)
Irregular Shapes
i.
Unlike the regular
shapes, irregular shapes cannot be accurately done using simple direct methods.
What you need to do is:
ii.
Divide the required
shape approximately into rectangles and triangles or even circles.
iii.
Calculate the area of
these shapes and add up the result.
iv.
Another method is to
divide the area into equal squares of known area.
v.
Then count the number of
full squares of known area and each part of a square as half square and then
add them together to get the total area. (half squares divide by two plus full
squares)
vi.
Instead of dividing the
area into equal squares, you can also trace the area to be measured.
vii.
Trace off the outline of
the area to be measured on square tracing paper and transfer the outline on
square paper.
viii.
Tick off all completed
squires in the outline and add up the total.
ix.
Mark with dots all the
half squares. Add up the total and divide by two.
x.
To get the total area
add up the number of complete squares and that of the half squares.
xi.
Using the map scale
provided, find the area of one square in order to calculate the approximate
total area.
Striping Method
a.
Trace the shape of the
area on paper to be measured.
b.
Draw stripes of uniform
width to cover the whole area.
c.
Calculate the areas of
each strip, which is a rectangle. The area obtained is the sum of individual
strips and should be given in the same units of the scale of the map.
d.
Find the area of the
rectangle and the two triangles, and then add up their areas.
