Geography: Class 12 (Part 3) — Chapter 3: Graphical Representation of Data

Introduction & Representation of Data

The transformation of data through visual methods like graphs, diagrams, maps, and charts is called representation of data. This graphic method enhances our understanding, makes comparisons easy, and creates a long-lasting imprint on the mind. It simplifies complex geographical distributions such as population growth, sex ratio, age-sex composition, and occupational structure within a territory.

General Rules for Drawing Graphs, Diagrams and Maps

1. Selection of a Suitable Method

Data characteristics must be matched with the appropriate graphical representation:

Line Graphs: Best suited for representing temperature, population growth over time, or continuous time-series data.
Bar Diagrams: Ideal for representing rainfall, commodity production, or discrete category comparisons.
Dot Maps: Suited for showing absolute population distribution (human or livestock).
Choropleth Maps: Best for representing density of population, literacy rates, or ratios.

2. Selection of Suitable Scale

The scale acts as a measure of the data. It must be carefully chosen to ensure the entire dataset is represented accurately, being neither too large nor too small.

3. Cartographic Design Components

Title: Indicates the name of the area, reference year, and the caption of the diagram. Usually placed at the top center.
Legend: Explains the colors, shades, symbols, and signs used. Typically positioned at the lower left or lower right.
Direction: Maps must show orientation, usually indicated by a North arrow symbol.

Construction of Diagrams

Diagrams are grouped based on their dimensions:

One-dimensional diagrams: Line graphs, polygraphs, bar diagrams, histograms.
Two-dimensional diagrams: Pie diagrams, rectangular diagrams.
Three-dimensional diagrams: Cube and spherical diagrams.

Line Graph & Polygraph

A Line Graph represents time-series data. A Polygraph is a line graph in which two or more variables are shown by an equal number of lines on the same axes for immediate comparison (e.g., comparing growth rates of different crops or sex ratios of different states).

Bar Diagrams

Also called columnar diagrams, drawn with columns of equal width. Types include:

Simple Bar Diagram: Used for immediate comparison of single variables.
Multiple Bar Diagram: Represents two or more variables together for comparison (e.g., male vs. female literacy rates).
Compound Bar Diagram: Different components of a single variable are stacked together in a single bar (e.g., sources of electricity generation: thermal, hydro, nuclear).

Pie Diagram

Also known as a Divided Circle Diagram. It represents the total value of an attribute using a circle divided into corresponding degrees of angle.

$$\text{Degree of Angle} = \frac{\text{Value of given State/Region}}{\text{Total Value}} \times 360$$

If data is in percentage form, the formula is:

$$\text{Degree of Angle} = \frac{\text{Percentage of } x \times 360}{100}$$

Example of export data distribution:

Unit/Region	% of Indian Export	Calculation	Degree
Europe	20.2	20.2 × 3.6	73°
Africa	6.5	6.5 × 3.6	23°
America	14.8	14.8 × 3.6	53°
Asia and ASEAN	56.2	56.2 × 3.6	203°
Others	2.3	2.3 × 3.6	8°
Total	100.0	-	360°

Flow Maps and Charts

A Flow Chart (or Dynamic Map) is a combination of a graph and a map. It is drawn to show the flow of commodities, vehicles, or people between places of origin and destination using lines of proportional width.

Requires a route map depicting transport routes and connecting stations.
Requires flow data (e.g., number of trains, passengers, or volume of goods).

Thematic Maps

Also known as distribution maps, these represent spatial variations of specific themes. They are classified into:

Quantitative Maps: Show measurable variations (e.g., rainfall, temperature, population density).
Non-quantitative Maps: Show non-measurable qualitative characteristics (e.g., soil types, vegetation zones).

Dot Maps

Used to show the distribution of absolute values (e.g., population, cattle). Each dot represents a specific quantity. Precautions include keeping all dots the same size and placing them accurately based on physiographic features (avoiding water bodies, high mountains, etc.).

Choropleth Maps

Drawn to depict data characteristics related to administrative units (e.g., density of population, literacy rates). Data is grouped into categories (usually 5) from very low to very high using the range formula:

$$\text{Range} = \text{Maximum Value} - \text{Minimum Value}$$

$$\text{Class Interval} = \frac{\text{Range}}{5}$$

Isopleth Maps

Derived from Iso (equal) and pleth (lines). An Isopleth Map joins places of equal values with imaginary lines. Common types include:

Isotherm: Equal temperature
Isobar: Equal pressure
Isohyet: Equal rainfall
Contour: Equal elevation

Drawing isopleths requires interpolation to find intermediate values between control points using the formula:

$$\text{Point of Isopleth} = \frac{\text{Distance between two points in cm}}{\text{Difference between the two values}} \times \text{Interval}$$