Formulae [1]
Formula: Point of Isopleth
\[\text{Point of Isopleth }=\frac{\text{Distance between two points in cm}}{\text{Difference between the two values of corresponding points}}\times\mathrm{Interval}\]
Key Points
Key Points: Construction of Diagrams > Pie Diagram
- Pie diagram represents the total value of data using a circle, and parts of the circle show different sub-values.
- It is also called a Divided Circle Diagram because the circle is divided into different sectors (angles).
- Each sector is made according to the share of each category (larger share = larger angle).
- To draw it, choose a suitable radius, divide the circle clockwise starting from smaller angles, and mark all sectors properly.
- Always add title, subtitle and legend, and ensure the circle is neither too big nor too small for clear presentation.
Key Points: Construction of Diagrams > Flow Maps/Chart
- A Flow Chart (Dynamic Map) is a combination of a map and graph, used to show the movement of goods, people or vehicles from one place to another.
- It represents data using lines of proportional width, where thicker lines show greater movement.
- It mainly shows:
Number and direction of vehicles
Number of passengers or quantity of goods transported - To prepare a flow map, we need:
A route map with origin and destination points
Data related to flow
A suitable scale to show quantity - Flow maps are widely used in transport and planning studies to show traffic density and movement patterns clearly.
Key Points: Construction of Diagrams > Bar Diagram
- Bar diagrams are drawn using vertical columns of equal width, so they are also called columnar diagrams.
- All bars must have the same width and should be placed at equal distance/intervals.
- Bars can be shaded with colours or patterns to make them clear and attractive.
- Simple Bar Diagram is used for easy comparison of one variable, and data is often arranged in ascending/descending order.
- Time series data in bar diagrams is shown in proper time order (months/years).
- Multiple Bar Diagram is used to compare two or more variables together (e.g., male-female literacy rates).
- Compound Bar Diagram shows different components within one bar, where each part represents a component of the total.
Key Points: Construction of Diagrams > Thematic Maps
- Graphs compare data, but thematic maps show regional distribution clearly.
- Need data + outline map + physical map.
- Must include area name, title, source/year, symbols, scale.
- Map should be well-planned and clear.
- Choose the correct method for mapping.
Key Points: Choropleth Map
- Choropleth maps show data related to administrative units like states or districts (e.g., population density, literacy rate, sex ratio).
- Requirements: outline map with boundaries and reliable statistical data for each unit.
- Data should be arranged in order and divided into five categories – very high, high, medium, low and very low.
- Categories are formed by calculating the range (maximum – minimum) and dividing it equally.
- Each category is shown using different shades or patterns, arranged from light (low) to dark (high), and the map must include proper design elements like title, legend and scale.
Key Points: Representation of Data
- Representation of data means presenting data through graphs, diagrams, maps and charts instead of only tables.
- Visual presentation makes it easier to understand and compare patterns like population growth, density, sex ratio, occupation, etc.
- The correct graphical method must be selected (e.g., line graph for change over time, bar diagram for rainfall/production, dot map for distribution, choropleth map for density).
- A suitable scale should be chosen carefully so that the data fits properly and is not too large or too small.
- Every map/diagram must include proper design elements like title, legend (index), and direction (north sign) for clarity.
Key Points: Classification of Thematic Maps based on Method of Construction
- Thematic maps are of two types: Quantitative (statistical) and Non-quantitative (qualitative).
- Dot maps are quantitative maps used to show distribution of population, cattle, crops, etc.
- Dots are of same size, and each dot represents a fixed value based on a chosen scale.
- Requirements: administrative map, statistical data, suitable dot scale, and relief/physiographic map.
- While plotting, keep boundaries light, and place fewer dots in mountains/deserts/snow regions.
Key Points: Isopleth Map
- Isopleth maps show continuous geographical data like temperature, rainfall, slope, etc., based on natural patterns (not administrative units).
- They use lines joining places of equal value, called isopleths (Iso = equal, pleth = lines).
- Common examples: Isotherm (temperature), Isobar (pressure), Isohyet (rainfall), Contours (height), Isobath (depth) etc.
- Requirements include a base map with point locations, correct data, and tools like a French curve for smooth lines.
- Interpolation is used to find intermediate values between two places, and isopleths are drawn using equal intervals (usually 5, 10 or 20).
Key Points: Construction of Diagrams > Line Graph
- Line graphs are mainly used to show time series data like temperature, rainfall, population growth, birth rate and death rate.
- Before drawing, data can be simplified by rounding off values for easy plotting.
- X-axis shows time (years/months) and Y-axis shows the data values (percentage, temperature, etc.).
- A proper scale should be selected on Y-axis, and it must include negative values if present.
- Values are plotted as dots and joined with a free-hand line; when multiple variables are shown using different line styles, it is called a polygraph.
