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Global Trends and Calculating Urban Growth

Over half the world's population now lives in cities, but this growth is not happening evenly across the globe. Developed countries generally have high levels of urbanisation but low growth rates, whereas emerging and developing countries have lower overall urbanisation but the fastest growth rates.

Urban populations expand due to two main factors: natural increase (which typically accounts for 60% of growth) and rural-to-urban migration (accounting for the remaining 40%).

Calculating Growth Rates

Geographers frequently use line graphs to track population changes over time and calculate the urban growth rate. You must be able to calculate both the percentage change and the mean annual rate of growth.

\text{Percentage Change} = \frac{\text{New Value} - \text{Old Value}}{\text{Old Value}} \times 100

Step 1: Identify the difference between the new and old values.

Difference = $14.8 - 11.5 = 3.3$ million

Step 2: Substitute the values into the equation.

$\text{Percentage Change} = \frac{3.3}{11.5} \times 100$

Step 3: Calculate and state the final answer with units (rounded to one decimal place if required).

$\text{Percentage Change} = 28.7\%$

\text{Mean Annual Growth Rate} = \frac{\text{Total Growth}}{\text{Number of Years}}

A city's population grew from 249,500 in 2011 to 263,700 in 2021. Calculate the mean annual rate of growth.

Step 1: Calculate the total growth.

Total growth = $263,700 - 249,500 = 14,200$

Step 2: Identify the total number of years.

Years = $2021 - 2011 = 10$ years

Step 3: Substitute into the equation and calculate with units.

$\text{Mean Annual Growth Rate} = \frac{14,200}{10} = 1,420$ people per year

Analysing Infrastructure Challenges

Imagine sharing a single square mile with over a million other people. This extreme density is the reality in Dharavi, a squatter settlement in the megacity of Mumbai. When rapid rural-to-urban migration exceeds a city's ability to build housing and services, it creates a severe infrastructure deficit.

To analyze these challenges, you must link the cause to the mechanism, and finally to the human impact:

Housing & Health: Migrants are forced to build temporary shelters on marginal land. Because these areas lack piped water (Lagos has only 14% piped water access), residents rely on unsafe sources, leading to water-borne diseases like cholera and typhoid.
Water Supply: In Mumbai, formal water infrastructure is so stretched that water is often only supplied for 2 hours per day.
Transport: Mumbai's road network is choked by 22 million registered vehicles, while the rail network is so dangerously overloaded that approximately 10 people die daily from falling off trains or crossing tracks.

Employment and the Informal Economy

When formal jobs cannot keep pace with thousands of new arrivals each day, people must create their own ways to survive. This leads to massive growth in informal employment and widespread underemployment. In developing and emerging cities, up to 93% of the workforce operates in this sector.

Despite being unofficial, the informal economy operates on a massive scale. In Dhaka, there are 500,000 rickshaw drivers providing vital paratransit, alongside 80,000 waste workers. In Dharavi, 15,000 single-room factories recycle 80% of Mumbai's plastic waste, generating an estimated annual turnover of between $650 million and $1 billion.

Because informal workers do not pay taxes, the government loses vital revenue. This creates a negative cycle where city authorities lack the funds to invest in much-needed public services like schools and health clinics.

Environmental Degradation and Pollution

The air in some rapidly growing cities is so thick with smog that simply breathing poses a daily hazard to human health. Unregulated industrial growth and poor sanitation lead to severe environmental degradation across air, water, and land.

Air Pollution: In Lagos, air pollution is 5 times higher than international limits due to old vehicles and wood cooking. In Mumbai, high levels of nitrogen oxides and PM2.5 cause widespread asthma and bronchitis.
Water Pollution: Without adequate sewage treatment, 800 million litres of raw sewage flows directly into Mumbai's Mithi River every day.
Waste Management: Lagos produces 13,000 tonnes of waste daily. Much of this ends up in massive dumps like the Olusosun landfill, where hundreds of rag pickers face life-threatening risks from toxic fires.

Investigating Spatial Growth Using GIS

If you look at satellite images of a city from twenty years ago and compare them to today, the physical expansion is undeniable. Geographers use multi-temporal imagery to visually track this urban sprawl and measure changes in the urban footprint over time.

Remote sensing captures data from satellites, which is then analyzed using a GIS (Geographic Information System). GIS works by layering different datasets over a base map. Because all data in GIS is georeferenced, multiple map layers can be stacked to identify spatial patterns.

For example, a geographer might layer an attribute like primary Environmental Quality (EQ) scores over secondary data showing the Index of Multiple Deprivation (IMD). By viewing these layers together, they can investigate if there is a correlation between the poorest urban areas (IMD Decile 1) and the lowest environmental quality.

Students often confuse urbanisation (the percentage of people living in cities) with urban growth (the raw speed or rate at which a city's population increases).

In 4-6 mark "Analyse" questions about urban challenges, examiners expect you to logically link the cause (e.g., rapid migration) to the mechanism (e.g., untreated sewage) and the final human impact (e.g., the spread of typhoid).

When calculating growth rates or interpreting line graphs, always include the correct units in your final answer (e.g., "%" or "people per year") and check if the mark scheme explicitly asks you to round to one decimal place.

If asked to explain the benefit of using GIS in an exam, always state clearly that it allows for the "layering of different data types" to "identify spatial patterns or relationships".

The process by which an increasing percentage of a country’s population comes to live in towns and cities.

The growth in population resulting only from the difference between birth rate and death rate (Births minus Deaths).

The speed at which an urban population increases over a specific period, usually expressed as a percentage or annual average.

Poor-quality, often illegal housing built on land not owned by the occupants, usually lacking basic services like piped water.

A city with a total population of over 10 million people.

The gap between the infrastructure a city needs (such as roads, water pipes, and schools) and the actual capacity available to its residents.

Unregulated, unofficial work where employees do not pay tax and have no legal protection or contracts.

When a job does not provide enough hours or income to survive, or when a worker is overqualified for the role they are performing.

Unofficial transport networks, such as rickshaws or mini-buses, that provide essential mobility but contribute heavily to congestion and smog.

The deterioration of the environment through the depletion of resources (air, water, soil) and the destruction of ecosystems.

Measures designed to protect public health, including the provision of clean piped water and the safe disposal of sewage and solid waste.

Satellite or aerial images taken of the same location on different dates, used to compare and provide visual evidence of change over time.

The rapid, often poorly planned spread of a city's built-up area into the surrounding countryside.

The physical area covered by a city’s buildings and infrastructure as seen from above.

The acquisition of data and imagery about the Earth's surface via satellites or high-altitude aerial photography.

A digital system for capturing, storing, and displaying data related to positions on Earth, allowing multiple layers of information to be analyzed together.

Information or data that has been tied to a specific location on the Earth's surface using coordinates (latitude and longitude).

A specific piece of data or numerical value (e.g., crime rate or population density) associated with a feature in a GIS layer.

A dataset used to measure relative poverty and living standards; in GIS, a low number (Decile 1) represents the highest level of deprivation.