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 Form 3 Geography: Statistical Methods online lessons

How to draw proportional circles using circles with areas proportional to the total square roots of the total values

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Answer Text:
PROPORTIONAL CIRCLES
-This is use of circles of various sizes to represent different sets of statistical data.
-Two approaches can be employed in construction of proportional circles
i) Using circles with diameters proportional to total values.
ii) Using circles with areas proportional to the total square roots of the total values.
Using circles with areas proportional to the total square roots of the total values.
Table showing mineral production In Kenya from year1998-2000
Steps
1. Determining the radii of circles by finding the square roots of the totals
1998 #sqrt1000#=31.62=32
1999 #sqrt1915=43.76#=44
2000 #sqrt3000#=54.77=55
2. Scale:1cm represents 10 tonnes
1998=3.2 cm
1999=4.4 cm
2000=5.5 cm
3. Using a pair of compasses draw circles of different radii representing mineral production in Kenya between 1998 and 2000.
4. Convert component values into degrees
1998: Graphite-200/1000×360=72◦
Fluorspar-#30/1000×360=10.8◦#
Soda ash-#270/1000×360=97.2◦#
Diamond-#500/1000×360=180◦#
1999: Graphite-#490/1915×360=92.1◦#
Fluorspar-#255/1915×360=47.9◦#
`#300/1915×360=56.4◦#
Diamond-#870/1915×360=163.6◦#
2000: Graphite-#930/3000×360=11.6◦#
Fluorspar-#450/3000×360=54◦ #
Soda ash-#350/3000×360=42.1◦ #
Diamond-#1270/3000×360=152.3◦#
5. On the proportional circle for each year use a protractor and mark out the angles
6. Shade the segments and then provide a key.


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