Selected options and fieldwork · Geographic inquiry and sampling

IB Diploma Programme Geography SL (first assessment 2019; 2017 guide). Besides the core, every student studies optional themes 选修主题: SL students study two of the seven options and HL students three. The options are examined in Paper 1. Every student also writes a fieldwork 野外考察 report on data they collect themselves: the internal assessment 内部评估 (IA). This topic gives each option's key ideas, processes and one case study, and then teaches the fieldwork method from question to conclusion.

In July 2021 more than 600 mm of rain fell on Zhengzhou in three days, close to the city's normal rainfall for a whole year. Water poured into underground train tunnels and roads became rivers. A few months later, coastal towns in England were still arguing about whether to build higher sea walls or let the sea take low farmland. The options study questions like these: how physical processes work, how they affect people, and how people manage them.

Must-know for options and fieldwork:

In Paper 1 each option has 20 marks. The first part is a set of short structured questions 结构化问题 (10 marks), often about a map, graph or table. Then you choose one of two essays (10 marks). SL students answer two options in 1 hour 30 minutes; HL students answer three in 2 hours 15 minutes.

The essays use the command terms examine, discuss, evaluate and to what extent. An essay answer needs a clear view, named examples with specific detail 具体细节 (places, dates, numbers), and a balanced judgement. "Floods are bad for people" earns little; "the 2021 Zhengzhou flood killed 380 people, including 14 passengers trapped in a flooded metro train" earns credit.

A drainage basin 流域 is the area of land that a river and its tributaries drain. Rain that falls on it can be stored (in soil, lakes and groundwater) or move to the river: over the surface (surface runoff 地表径流) or more slowly through the soil and rock.

A storm hydrograph 暴雨水文曲线 shows how a river's discharge 流量 (the volume of water passing a point each second) changes after a storm. Discharge rises along the rising limb 上升段 to a peak 洪峰 and falls along the falling limb. The time from peak rainfall to peak discharge is the lag time 滞后时间.

Cities shorten the lag time and raise the peak. Concrete and roofs do not let water soak in, and drains carry it quickly to the river. Steep slopes, saturated soil and a small, round basin have the same effect; forests and gentle slopes slow water down.

Flood management 洪水管理 can be hard or soft:

Case study: the Three Gorges Dam. The dam on the Yangtze (main body finished in 2006, fully working by 2012) stores flood water, generates about 22.5 GW of electricity and lets large ships reach Chongqing. About 1.3 million people were moved from the land the reservoir covered, and the dam traps sediment that once built up land downstream. China's sponge city 海绵城市 programme (started 2015) is a soft response for cities: parks, wetlands and porous pavements that hold rain where it falls.

Waves shape coasts. They erode rock by hydraulic action 水力作用 (water and air forced into cracks) and abrasion 磨蚀 (rocks thrown against the cliff). Where waves lose energy, they deposit sand and shingle as beaches and spits 沙嘴. Where hard and soft rocks meet the sea, the soft rock is eroded into bays and the hard rock is left as headlands; caves, arches and stacks form at the headlands.

Longshore drift 沿岸漂移 moves sand along the coast in the direction of the main wind and waves. This is why coastal defences in one place affect the next place.

Case study: the Holderness coast, England. Its soft clay cliffs lose about 2 m a year on average, one of the fastest rates in Europe. Groynes built at Mappleton in 1991 protected the village, but the cliffs to the south then eroded faster because they received less sand. At Medmerry (2013) the sea defences were moved inland, and the new salt marsh now protects homes and is a habitat for birds. A good essay weighs who gains and who loses from each choice.

Extreme environments 极端环境 are cold (high mountains, polar and glacial areas) or dry (hot deserts). Ice erodes valleys into a U shape and leaves piles of rock called moraines 冰碛. In hot deserts, wind builds dunes and rare flash floods cut steep valleys called wadis.

People see these places as both opportunities 机遇 (minerals, tourism, solar energy, scientific research) and challenges 挑战 (cold or heat, little water, poor access, a fragile environment).

Case study: the Qinghai-Tibet Railway (opened 2006). Much of the line crosses permafrost 永久冻土, ground that stays frozen all year. Heat from a train track could melt it and make the track sink, so engineers built bridges and used pipes that carry heat out of the ground. The railway brings tourists and trade to Tibet; it also brings pressure on a fragile environment and on local culture.

The Earth's surface is broken into tectonic plates 构造板块 that move a few centimetres a year. Most volcanoes and earthquakes happen at plate margins 板块边缘:

Hazard risk 灾害风险 grows with three things: how strong and frequent the hazard is, how many people and buildings are in its path (exposure 暴露度), and how easily they are harmed (vulnerability 脆弱性). Poverty, weak buildings and poor warning systems raise vulnerability.

The model explains why similar events have very different results. The 2010 Haiti earthquake (magnitude 7.0) killed more than 100,000 people, because many buildings were weak and the capital was close to the epicentre 震中. The 2011 Tōhoku earthquake in Japan (magnitude 9.0) released about 1,000 times more energy. Strong buildings and early warnings saved many lives, but the tsunami was higher than many sea walls and about 18,000 people died or were never found.

The Butler model 巴特勒模型 describes how a tourist destination changes over time. A few visitors explore it; local people start to provide services; companies build hotels and visitor numbers grow fast. Growth slows as the place reaches its carrying capacity 承载力, the number of visitors it can take before the environment or visitor experience suffers. Then it stagnates, and either declines or is rejuvenated by new investment.

Case study: Venice. Fewer than 50,000 people live in the historic centre, but on busy days it receives far more visitors than residents. Overtourism 过度旅游 raises rents, pushes residents out and crowds the streets. Venice has stopped large cruise ships from sailing through the city centre (2021), limited tour groups to 25 people (2024) and charged day visitors an entry fee on the busiest days (since 2024). Critics ask whether a fee of a few euros changes behaviour or only raises money.

Food security 粮食安全 means that all people can get enough safe and healthy food at all times. A famine 饥荒 often happens not because there is no food, but because people cannot afford or reach it. The economist Amartya Sen argued that in the Bengal famine of 1943 food was available, but prices rose far faster than the wages of the poor. This links to the "access" pillar of food security in topic 02.

As countries develop, the main causes of death change. This is the epidemiological transition 流行病学转变: deaths from infectious diseases (such as diarrhoea and tuberculosis) fall, people live longer, and non-communicable diseases 非传染性疾病 (heart disease, cancer, diabetes) become the main causes of death. Cheap high-calorie food and less physical work also raise obesity 肥胖. China has made this change within one lifetime: life expectancy rose from about 59 years in 1970 to about 79 years in 2023.

More than half of the world's people live in cities. A megacity 特大城市 has more than 10 million people. Shenzhen grew from a small border town in 1980 to about 17.6 million people in the 2020 census.

Land-use models 土地利用模型 describe how a city is arranged. Burgess's model shows rings around the centre; Hoyt's model shows sectors along transport routes. Use them as ideas to test against a real city, not as truths.

Fast growth causes urban stress 城市压力: housing shortages, traffic congestion, air pollution and waste. Responses include public transport, new housing and urban regeneration 城市更新, which turns old industrial land into new homes, offices and parks. A good evaluation asks who benefits: regeneration can raise rents and push poorer residents out.

The fieldwork report is worth 25% at SL and 20% at HL. It is a report of up to 2,500 words, marked out of 25, on primary data 一手数据 that you collect yourself in the field.

You cannot measure everything, so you take a sample:

Worked example. Question: Does the number of pedestrians fall with distance from the central square? Hypothesis: pedestrian numbers fall as distance increases. Null hypothesis: there is no relationship. The student counted pedestrians for 2 minutes every 100 m along one street (systematic sampling).

Here $d$ is the difference between the two ranks, $n = 8$ and $\sum d^2 = 158$. Spearman's rank correlation 斯皮尔曼等级相关 is

The value is negative, so pedestrian numbers fall as distance rises. For $n = 8$, the critical value at the 5% level (two-tailed) is 0.738. Because 0.88 is bigger than 0.738, we reject the null hypothesis: the relationship is statistically significant 统计显著. This does not prove that distance causes the change: shops are also closer to the square.

For counts in categories, use a chi-squared test 卡方检验 instead. For a table with two rows and two columns there is 1 degree of freedom, and the critical value at the 5% level is 3.84; a result of 5.2 is above it, so the two variables are not independent.

Evaluation of the worked example: one street, one weekday morning and one 2-minute count per site. Better: several streets, counts at different times and days, and two or three counts at each site.

• Paper 1: 20 marks per option (structured questions and one essay); specific detail in every essay.
• Freshwater: the storm hydrograph and lag time; why cities flood faster; hard and soft management; the Three Gorges Dam and sponge cities.
• Coasts: hydraulic action and abrasion; longshore drift; the strategies and their problems; Holderness, Mappleton and Medmerry.
• Extreme environments: glacial and desert landforms; opportunity against challenge; the Qinghai-Tibet Railway on permafrost.
• Hazards: the three plate margins; risk from hazard, exposure and vulnerability; Haiti 2010 against Tōhoku 2011.
• Tourism: Butler's stages and carrying capacity; Venice's controls.
• Food and health: famine as a failure of access; the epidemiological transition.
• Urban: megacities; Burgess and Hoyt as models to test; urban stress and regeneration.
• Fieldwork: the inquiry stages; the three sampling methods; the Spearman's rank calculation and its critical value; chi-squared; the six IA criteria.