Dot and Sphere Diagram// Practical Geography //GEOA//CC2
Dot and Sphere Diagram is generally used to represent Rural and Urban population respectively at one go. However dots can be used separately and sphere can be used separately in different diagrams to represent other aspects.
Sphere generally is used to represent volume specifically when the data is disproportionately large and cannot be represented properly by using and two dimensional diagram. Sphere thIs is a 3D dimensional diagram.
When dot and sphere is used together in one diagram to represent rural and urban population. sphere is used to represent urban population as very large population is concentrated in avery small areal unit i.e. a town or city which is represented often by a singula rmarker on a map. Whereas rural population is represented as being distributed over a larger spatial unit compared to a town or a city.
Advantages and disadvantages of dot maps
Advantages
Dot maps are easy readable, also for laymen
Are perfectly suitable to show density distributions
By counting the symbols it is possible to determine the original data
Disadvantages
The data have to be georeferenced with coordinates
The map design is time-consuming and expensive
Sum and Solution (table-1)
|
block.no. |
Block |
Rural
Population |
Urban Population |
Rural Population(to scale)1dot=6000 persons |
Radii of Sphere R= 3√(3×T.U.)/4π) |
Radii of Spheres to Scale |
|
1 |
Darjiling- Pulbazar |
115837 |
114204 |
19.30616667 |
30.09753319 |
0.752438 |
|
3 |
MIRIK |
42437 |
9141 |
7.072833333 |
12.9708479 |
0.324271 |
|
4 |
Kurseong |
72204 |
13663 |
12.034 |
14.83038708 |
0.37076 |
|
5 |
Matigara |
123921 |
65123 |
20.6535 |
24.95831509 |
0.623958 |
|
2 |
Rangli Rangliot |
64349 |
0 |
10.72483333 |
0 |
0 |
|
6 |
Kharibari |
88230 |
0 |
14.705 |
0 |
0 |
Calculation for Scale of Sphere
|
Sl.no. |
Urban population |
Radii
of Sphere R= 3√(3×T.U.)/4π) |
Radii to scale 1cm=40 units |
|
1 |
115000 |
30.16729779 |
0.754182 |
|
2 |
50000 |
22.85390749 |
0.571348 |
|
3 |
9000 |
12.90381021 |
0.322595 |
Another example of Sphere Diagram
Use
the data given in the table bellow and draw a Sphere diagram to show the urban
population in P.S of Maldah district (2001).
Principle :
Volume of Sphere 4 𝜋𝑟3=
P(Urban Population)
CALCULATION
TABLE FOR SPHERE DIAGRAM
|
SL
NO. |
POLICE STATION |
URBAN POPULATION(P) |
3 3∗𝑃 𝑟 = √ 4∗𝜋 |
SCALE |
RADIUS OF SPHERE (cm.) |
|
1 |
Harischandrapur |
222000 |
37.56 |
1cm to 70 units |
0.53 |
|
2 |
Kharba |
219000 |
37.38 |
0.53 |
|
|
3 |
Ratua |
241000 |
38.60 |
0.55 |
|
|
4 |
Gajal |
182000 |
35.15 |
0.50 |
|
|
5 |
Bamongola |
300000 |
41.52 |
0.59 |
|
|
6 |
Habibpur |
142000 |
32.36 |
0.46 |
|
|
7 |
Englishbazar |
242000 |
38.65 |
0.55 |
|
|
8 |
Manikchak |
150000 |
32.96 |
0.47 |
|
|
9 |
Kaliachak |
451000 |
47.57 |
0.68 |
|
|
10 |
Maldah |
1200000 |
65.92 |
0.94 |
STEP-2
CALCULATION TABLE FOR PROPORTIONAL SCALE
|
SL NO. |
URBAN POPULATION(P) |
3 3∗𝑃 𝑟 = √ 4∗𝜋 |
SCALE |
RADIUS OF SPHERE (cm.) |
|
1 |
1200000 |
65.92 |
1cm to 70 units |
0.94 |
|
2 |
670000 |
54.28 |
0.76 |
|
|
3 |
140000 |
32.21 |
0.46 |
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