Graphical Representation of Data

A dot map is used to show the distribution of phenomena like population, cattle and crops. The chapter states that population distribution is suitably represented on dot maps.

The chapter says line graphs are usually drawn to represent time series data related to population growth. Since decadal growth of population is time-based data, the best suited diagram is a line graph.

A polygraph is defined in the chapter as a line graph in which two or more than two variables are shown by an equal number of lines for comparison. So the correct answer is more than two variables.

The chapter says a flow chart is also called a Dynamic Map. Therefore, the map known as “Dynamic Map” is the flow map.

A thematic map is a map drawn to show the distribution or variation of a particular theme or characteristic over an area. The chapter says such maps help us understand patterns of regional distribution or variations over space, and are also called distribution maps.

A multiple bar diagram is used to represent two or more variables side by side for comparison, with separate bars for each variable. A compound bar diagram shows the different components of one total in a single bar, divided into rectangular parts. So, multiple bars compare separate variables, while compound bars show parts of one whole.

The requirements for a dot map are:
- an administrative map of the area showing state/district/block boundaries,
- statistical data on the selected theme for the units,
- selection of a scale to decide the value of one dot,
- and a physiographic map of the region, especially relief and drainage maps.

The chapter also says the boundary lines should not be too thick and all dots should be of the same size.

To construct a traffic flow map:
1. Take an outline map of the area with routes and nodal stations.
2. Collect data on the flow of goods, passengers, vehicles, etc., between origin and destination.
3. Select a scale to represent the quantity.
4. Draw lines of proportional width on the routes according to the numbers.
5. Add a terraced scale as legend and mark stations with suitable symbols.

The chapter gives the Delhi railway routes as an example.

An Isopleth map is a map in which lines of equal value are drawn to show continuous variation in data such as temperature, rainfall, pressure, or height. Examples are isotherms, isobars, isohyets and contours.

Interpolation means finding intermediate values between observed stations. The chapter says to:
1. determine the minimum and maximum values,
2. find the range,
3. choose a suitable interval like 5, 10, or 20,
4. then locate the exact point using the formula:
$$\text{Point of Isopleth} = \frac{\text{Distance between two points in cm}}{\text{Difference between the two values of corresponding points}} \times \text{Interval}$$
The isopleth is then drawn through these interpolated points.

To prepare a choropleth map:
1. Take a map showing the administrative units.
2. Arrange the data in ascending or descending order.
3. Find the range = maximum value − minimum value.
4. Divide the range into 5 categories: very low, low, medium, high, very high.
5. Assign shades, patterns or colours in increasing or decreasing order.
6. Complete the map with proper title, legend, source and scale.

The chapter also shows an example using literacy rates in India.