Specialised diagrams: climographs, pyramids, Lorenz curves and ternary diagrams

Detail

These four diagrams go beyond the NCERT chapter. Geography and economics answers use them often, because each one sums up a complex pattern in a single picture.

1. Climograph (Griffith Taylor)

• Climograph: a graph that shows the climate of one place as a 12-sided shape. Each corner of the shape is one month.
• Who made it: Griffith Taylor, an Australian geographer. He used it to compare how comfortable different climates are for human living and settlement.
• Axes in Taylor's original climograph:
• Vertical (Y) axis → mean monthly wet-bulb temperature. This is the temperature read by a thermometer whose bulb is wrapped in wet cloth. Evaporation cools the bulb, so the reading also reflects humidity. It is a better guide than air temperature to how hot a place feels.

• Horizontal (X) axis → mean monthly relative humidity (the amount of water vapour in the air, as a percentage of the most the air could hold at that temperature).

• How it is drawn (step by step):

• Plot one point for each month, from January to December.
• Join the points in order, and join December back to January.

• The closed 12-sided polygon is the climograph.

• Taylor's four corners: these are his own labels for the four corners of the graph.

• Scorching = hot and dry
• Muggy = hot and humid
• Raw = cold and humid
• Keen = cold and dry

2. Hythergraph — the climograph's cousin

• Hythergraph: monthly temperature (Y axis) plotted against monthly rainfall (X axis). The 12 points are joined in the same way.
• It is easier to draw because rainfall and temperature data are recorded everywhere. Most school and university atlases use this form. It is often loosely called a "climograph" too.

Feature	Climograph (Taylor)	Hythergraph
Y axis	Wet-bulb temperature	Air temperature
X axis	Relative humidity	Rainfall
Main use	How comfortable a climate is for people	Comparing climate types
Output	12-sided polygon	12-sided polygon

3. Reading climate from the shape

Climate	Shape of the polygon	Why
Equatorial (Singapore, Congo Basin, Amazon; within about 5°–10° of the equator)	Tight, small cluster at the hot and wet corner	Temperature and rainfall stay high in every month, so the 12 points sit close together
Monsoon (Mumbai, Kolkata, Chennai-type stations)	Long, narrow loop stretched along the rainfall axis	Temperature changes only a little, but rainfall jumps from almost nothing (December–May) to very high (June–September)
Mediterranean (Rome, Perth)	Slopes the "wrong" way: hot months are dry, cool months are wet	Rain comes in winter from westerly cyclones. In summer the subtropical high-pressure belt keeps the air dry
Hot desert (Sahara, Thar)	Hugs the low-rainfall edge and stretches up and down	Very little rain. Large swings in temperature between seasons

• Monsoon loop, cause → process → result:
• In summer the land heats faster than the sea → low pressure forms over north-west India.
• Moist south-west winds are drawn in from the Indian Ocean → heavy rain falls from June to September, while temperature changes only slightly.
• Result: the points spread far apart along the rainfall axis. This gives the long, narrow loop.

4. Population pyramid

• Population pyramid (age-sex pyramid): two sets of horizontal bars placed back to back.
• Males are on the left and females on the right.
• Each bar is one age group, usually 5 years wide (0–4, 5–9 … 80+).

• Bar length = the share (%) of the total population in that age and sex group.

• Where the data comes from in India: the age-sex tables of the Census (latest full count: Census 2011) and the yearly Sample Registration System (SRS).

Pyramid shape	What it looks like	What it means	Example
Expansive	Wide base, narrow top	High birth rate and high fertility; a young population	Bihar; many countries in Sub-Saharan Africa
Stationary / bell	Sides nearly straight up to old ages	Low birth and death rates; slow growth	Many West European countries
Constrictive (ageing)	Narrow base, wider middle and top	Fertility below replacement level; more old people	Kerala, Japan

• Why Kerala's pyramid narrows at the base:
• High female literacy and good health care → fewer infant deaths and a later age at marriage.
• Families choose to have fewer children → each new age group born is smaller than the one before.

• People also live longer → the top of the pyramid widens. The result is an ageing population (a rising share of people aged 60 and above).

• Exam use: the pyramid shows the dependency ratio (people aged 0–14 and 60+ for every 100 people aged 15–59, the working ages). It also shows the demographic dividend, the economic gain possible while the working-age share is at its largest.

5. Lorenz curve

• Lorenz curve: a graph that shows how unevenly something is shared. It was proposed by the American economist Max O. Lorenz in 1905.
• How it is drawn (step by step):
• Arrange people, households or areas from the poorest (smallest share) to the richest (largest share).
• X axis → the cumulative % (running total) of people or areas, from 0 to 100.
• Y axis → the cumulative % of the quantity they hold. This can be income, land, consumption or industrial output.

• Plot the points and join them. The curve always starts at (0, 0) and ends at (100, 100).

• Line of equality: the straight 45° diagonal. On it, every 10% of people holds exactly 10% of the quantity.

• Reading it: the more the curve bows away (sags) from the diagonal, the greater the inequality or concentration.
• Geography uses:
• How concentrated industry is across districts or states.
• How land is spread across operational holdings, where a few large holders own much of the land.
• How unevenly population is spread across a region's area.
• In each case it shows whether an activity is dispersed (spread out) or concentrated (bunched together).

6. Gini coefficient

• Gini coefficient: a single number that measures inequality, taken from the Lorenz curve. It was developed by the Italian statistician Corrado Gini (1912).
• Gini = (area between the line of equality and the Lorenz curve) ÷ (total area under the line of equality).
• 0 = perfect equality (the curve lies on the diagonal).

• 1 = total concentration (one unit holds everything).

• India — consumption inequality (Household Consumption Expenditure Survey, HCES, by MoSPI):

• The survey's fieldwork ran from August 2023 to July 2024 [2].
• Rural Gini: 0.266 (2022-23) → 0.237 (2023-24) [2].
• Urban Gini: 0.314 (2022-23) → 0.284 (2023-24) [2].
• Inequality fell in both rural and urban areas, and urban inequality stays higher than rural [2].

• Average MPCE (Monthly Per Capita Consumption Expenditure: the average spending per person per month) in 2023-24 was Rs 4,122 in rural areas and Rs 6,996 in urban areas [2].

• Watch out: a Gini based on consumption is usually lower than one based on income or wealth. This is because rich households save a large part of their income instead of spending it.

7. Ternary diagram

• Ternary (triangular) diagram: an equilateral triangle used for data with three parts that always add up to 100%.
• Each corner = 100% of one part.
• The side opposite that corner = 0% of that part.

• Any point inside the triangle stands for one mix of all three parts.

• How to read a point (step by step):

• Follow the grid lines that run parallel to the side opposite each corner.
• Read the three percentages.

• Check that they total 100. If not, the point has been read wrongly.

• Soil texture triangle (USDA):

• The three parts are sand (2–0.05 mm), silt (0.05–0.002 mm) and clay (less than 0.002 mm).
• The triangle is split into 12 texture classes: sand, loamy sand, sandy loam, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay and clay.
• Loam is a balanced mix (roughly 40% sand, 40% silt, 20% clay). It is the best texture for farming.

• Indian links: the black (regur) soils of the Deccan Plateau, rich in clay, fall in the clay corner. The alluvial soils of the Indo-Gangetic plain fall in the loam to silt-loam classes.

• Workforce triangle:

• The three parts are the primary (farming, mining), secondary (manufacturing) and tertiary (services) sectors.
• Agrarian economies sit near the primary corner. Post-industrial economies sit near the tertiary corner.
• A country's path over the decades shows its sectoral shift (the movement of workers from one sector to another).

Prelims Hooks

• Taylor's climograph plots wet-bulb temperature against relative humidity. The hythergraph plots temperature against rainfall. Do not swap the two.
• Climograph shapes: equatorial = tight cluster. Monsoon = long, narrow loop. Mediterranean = hot months dry, cool months wet.
• Taylor's four corners: scorching (hot-dry), muggy (hot-humid), raw (cold-humid), keen (cold-dry).
• Wide base of the pyramid → high fertility (Bihar). Narrow base and wider top → ageing (Kerala, Japan).
• Lorenz curve (1905, Max Lorenz): the further it bows from the line of equality, the greater the inequality.
• Gini coefficient = gap area ÷ area under the diagonal. 0 = perfect equality, 1 = total concentration.
• HCES 2023-24: rural Gini 0.237, urban Gini 0.284. Both fell from 2022-23 (0.266 and 0.314) [2].
• A ternary diagram needs three parts that add up to 100%. It cannot show two parts or four parts.
• The USDA soil texture triangle has 12 classes. Loam is a balanced sand–silt–clay mix.
• Trap: a "triangle" for population, area and density is not ternary. Those three values do not add up to 100%.

Mains Points

• Regional inequality: Lorenz curves and Gini values for income, land or industrial output show concentration. Examples are industry bunched in Maharashtra, Gujarat and Tamil Nadu, and land held in few hands in some states. These make a strong case for balanced regional development. The HCES 2023-24 fall in Gini (rural 0.237, urban 0.284) suggests that consumption gaps are narrowing [2].
• Demographic contrasts: the expansive pyramid of Bihar and the constrictive pyramid of Kerala show that India is going through the demographic transition at different speeds. North Indian states need jobs and skilling to use their demographic dividend. Southern states need pensions, elderly care and health insurance.
• Climate diagnosis: a hythergraph's long monsoon loop shows how much India depends on 3–4 rainy months. That dependence is why irrigation, groundwater recharge and crop insurance matter for farming. A change in the shape of the polygon over the decades can also signal climate change.
• Soil and land use: soil texture triangles guide decisions on irrigation, crop choice and soil health management. Clay-rich regur holds water well, which suits cotton grown without irrigation. Sandy soils in arid Rajasthan need moisture conservation.