GCE A/L Geography cheat sheet

Plate boundaries: divergent (constructive) plates move apart, new oceanic crust forms at mid-ocean ridges; convergent (destructive) plates collide, producing subduction zones, trenches and volcanic arcs; transform (conservative) plates slide past each other, producing fault lines but little volcanism.

Sea-floor spreading rate equals distance from ridge axis divided by magnetic anomaly age; symmetrical magnetic striping either side of a ridge records reversals of Earth's field.

Subduction occurs where oceanic lithosphere is denser than underlying asthenosphere; ocean-ocean convergence gives island arcs, ocean-continent gives volcanic mountain chains such as the Andes.

Earthquake magnitude (Moment Magnitude Scale) is logarithmic: each whole number is about 31.6 times more energy released; intensity scales (Modified Mercalli) describe observed damage, not energy.

Volcanic explosivity is controlled mainly by magma viscosity and dissolved gas: high-silica (rhyolitic) magma is viscous and explosive; low-silica (basaltic) magma is fluid and effusive, producing shield volcanoes.

Hotspots form where a mantle plume intersects the lithosphere; chains of progressively older volcanoes (e.g. Hawaii) record plate motion direction and rate.

Hazard risk = (hazard probability x exposure x vulnerability) / capacity to cope; the same event produces different disaster outcomes depending on population density, building codes and preparedness.

Landforms of folding and faulting: anticlines and synclines from compressional folding; horsts and grabens from tensional normal faulting; thrust faults from compression.

Wave energy depends on fetch, wind speed and wind duration; longer fetch produces higher-energy waves and larger sediment transport.

Constructive (spilling) waves have low height, long wavelength and strong swash, building beaches; destructive (plunging) waves have high height, short wavelength and strong backwash, eroding beaches.

Longshore drift moves sediment in the direction of the dominant swash, at right angles to the backwash; drift direction changes with prevailing wind and wave approach.

Erosion processes: hydraulic action (wave force compressing air in cracks), abrasion (sediment scouring), attrition (clasts wearing each other), solution (chemical weathering).

Concordant coasts have strata parallel to the coast, giving cliffs and few bays; discordant coasts have strata perpendicular to the coast, giving headlands and bays.

Coastal landform sequence: cliff, wave-cut notch, wave-cut platform; cave, arch, stack, stump; spit and bar form where drift is interrupted or the coastline changes direction.

Sediment budget: inputs (river, cliff erosion, offshore, longshore drift) minus outputs (offshore loss, subaerial erosion, human removal) determines whether a coast advances or retreats.

Hard engineering (sea walls, groynes, riprap) reduces local erosion but can increase erosion downdrift by starving sediment supply; soft engineering (beach nourishment, dune stabilisation, managed retreat) works with natural processes.

Glacier mass balance = accumulation (snowfall, avalanches, wind deposition) minus ablation (melting, sublimation, calving); a positive balance advances the snout, a negative balance retreats it.

Erosion mechanisms: abrasion (rock fragments grinding bedrock), plucking (meltwater refreezing around bedrock and tearing it away), and meltwater erosion.

Erosional landforms: cirque (armchair hollow), arête (sharp ridge between cirques), pyramidal peak (hanging arêtes), U-shaped valley, hanging valley, roche moutonnée.

Depositional landforms: till (unsorted, angular), moraine (terminal, lateral, medial, recessional), drumlin (streamlined mound with stoss and lee), esker (sinuous ridge of meltwater gravel), outwash plain (sorted, rounded sediment).

Periglacial processes: freeze-thaw weathering, frost heave, solifluction (slow saturated soil flow over permafrost), nivation (snow-patch erosion), patterned ground and pingos.

Permafrost is ground remaining below 0 degrees C for at least two consecutive years; active layer thaws seasonally and is prone to thermokarst collapse when permafrost degrades.

Glacial trough cross-profile is U-shaped with steep sides and a flat floor; a river valley is V-shaped, reflecting the difference between ice and water erosion.

Ice cores preserve trapped air bubbles that record past atmospheric composition; oxygen isotope ratios (delta-18O) indicate past temperature and ice volume.

Hydrological cycle stores: oceans (about 97% of water), glaciers and ice caps, groundwater, surface water, atmosphere, soil moisture and biota; fluxes are evaporation, evapotranspiration, condensation, precipitation, runoff and infiltration.

The water balance equation: P = Q + E +/- delta S, where P is precipitation, Q is runoff, E is evapotranspiration and delta S is change in storage.

A storm hydrograph shows rising limb, peak discharge, recession limb and lag time; urbanisation, impermeable rock, steep slopes, saturated soils and deforestation shorten lag time and raise peak discharge.

Drainage basin characteristics: drainage density (channel length per unit area), bifurcation ratio, stream order (Strahler), and the shape of the basin affect flood response.

Groundwater: the water table is the upper limit of saturation; an aquifer is permeable rock storing water; a confining layer (aquiclude) restricts flow, creating artesian conditions.

Water scarcity is physical (supply below demand) or economic (lack of infrastructure and investment to make available water usable); water stress is measured per capita availability, commonly below 1,700 cubic metres per person per year.

Virtual water is the water embedded in production of goods; importing water-intensive crops shifts water demand between countries.

Flood management: hard defences (dams, levees, channel straightening) versus soft strategies (afforestation, wetland restoration, floodplain zoning, catchment management).

Atmospheric structure: troposphere (weather, temperature falls with height), stratosphere (ozone layer, temperature rises with height), mesosphere, thermosphere.

Global energy budget: incoming shortwave solar radiation balances outgoing longwave radiation; greenhouse gases absorb and re-emit longwave radiation, warming the lower atmosphere.

Natural climate drivers: Milankovitch cycles (eccentricity, obliquity, precession), solar output variation, volcanic aerosols (short-term cooling) and ocean circulation (ENSO, thermohaline circulation).

Enhanced greenhouse effect is driven by anthropogenic emissions of carbon dioxide, methane, nitrous oxide and halocarbons; radiative forcing is measured in watts per square metre.

Climate feedbacks: positive (permafrost methane release, reduced albedo from ice melt, water vapour increase) amplify warming; negative (increased cloud albedo, carbon uptake by oceans and forests) dampen it.

Weather systems: depressions form at polar fronts along the jet stream with warm and cold sectors; anticyclones bring settled weather, with winter fog and summer drought.

Urban heat island: cities are warmer than surrounding rural areas due to low albedo surfaces, reduced evapotranspiration and anthropogenic heat release; strongest at night.

Climate proxies: ice cores, tree rings (dendrochronology), pollen analysis, ocean sediment cores, historical records and instrumental data, each with different resolution and reliability.

Demographic Transition Model stages: high stationary (high birth and death rates), early expanding, late expanding, low stationary, and declining; natural increase = birth rate minus death rate.

Population growth rate = (natural increase + net migration) / total population; doubling time approximates 70 divided by annual percentage growth rate.

Population pyramid shape indicates structure: broad base and narrow top indicate a youthful population with high dependency; narrow base indicates an ageing population.

Dependency ratio = (population aged under 15 plus over 64) / (population aged 15 to 64), expressed per 100 working-age people.

Push factors drive migration from origin (poverty, conflict, environmental hazard, unemployment); pull factors attract to destination (jobs, services, safety, family ties).

Migration models: Ravenstein's laws (short-distance moves, step migration, urban pull), Lee's push-pull model, and the migration transition linked to development stage.

Settlement hierarchy: hamlet, village, town, city, conurbation, megacity; higher-order settlements have larger spheres of influence, greater range and threshold populations.

Rural-urban migration and natural increase drive urban growth; counter-urbanisation moves population from cities to rural areas, often driven by housing cost and quality of life.

Urbanisation is the increasing proportion of a population living in urban areas; it is driven by rural-urban migration and natural increase, and is fastest in low-income countries.

Urban land-use models: Burgess concentric zone, Hoyt sector, Harris and Ullman multiple nuclei, and the Latin American and African city models reflecting colonial and informal settlement patterns.

Bid-rent theory explains land use by distance from the central business district: retail and offices outbid other uses at the centre, residential uses further out.

Urban processes: suburbanisation, counter-urbanisation, re-urbanisation (gentrification), decentralisation of employment and edge-city growth.

Informal settlements (slums, shanty towns) arise from rapid in-migration outpacing housing supply; upgrading strategies include site and service schemes, tenure legalisation and self-help housing.

Sustainable urban management: transport-oriented development, green infrastructure, congestion charging, waste recycling, urban greening and compact city design.

Urban regeneration involves public-private partnership, flagship projects and cultural-led renewal; it can displace existing residents through gentrification.

Measuring urban change: index of segregation, index of dissimilarity, population density, land-use mapping and census tract analysis.

Globalisation is the increasing interconnectedness of economies and societies through trade, capital flows, information, migration and cultural exchange.

Trade theories: comparative advantage (specialisation raises total output), and the new trade theory (economies of scale and agglomeration drive trade patterns).

Balance of trade = value of exports minus value of imports; a surplus is positive, a deficit negative.

Terms of trade = (index of export prices / index of import prices) x 100; a decline means a country must export more to buy the same imports.

Trading blocs: free trade areas, customs unions, common markets and economic unions, each with increasing integration; the EU is an example of a single market.

Development indicators: GDP per capita, Human Development Index (life expectancy, education, income), Gini coefficient (inequality), Multidimensional Poverty Index.

Development models: Rostow's stages of growth, dependency theory, core-periphery model, and the Brandt line dividing richer north from poorer south.

Transnational corporations (TNCs) drive foreign direct investment and global production networks; they can create jobs and technology transfer but also exploit cheap labour and repatriate profits.

Resource security means reliable access to sufficient resources at affordable prices; insecurity arises from scarcity, geopolitics, price volatility and supply concentration.

Energy mix: fossil fuels (coal, oil, gas), nuclear and renewables (hydro, wind, solar, geothermal, biomass); energy security improves with diverse, domestic and low-carbon supplies.

Energy demand per capita rises with industrialisation and income; energy intensity measures energy used per unit of GDP.

Food security exists when all people have physical and economic access to sufficient, safe and nutritious food; it is affected by availability, access, utilisation and stability.

Food production systems: subsistence, commercial, intensive and extensive; the Green Revolution raised yields through high-yield varieties, irrigation and fertiliser but increased inequality and environmental costs.

Water-food-energy nexus: producing food and energy requires water, and treating and moving water requires energy, so policies in one area affect the others.

Resource depletion: reserves are economically recoverable resources; peak production (Hubbert curve) occurs when extraction reaches maximum before decline.

Strategies for resource security: diversification of supply, stockpiling, recycling, substitution, efficiency improvements and international agreements.

Sampling methods: random (unbiased, may miss patterns), systematic (regular interval, good for gradients), stratified (proportional to sub-groups); sample size affects reliability.

Measures of central tendency (mean, median, mode) and dispersion (range, interquartile range, standard deviation) summarise data; standard deviation shows spread around the mean.

Spearman's rank correlation coefficient: rho = 1 - (6 x sum of d squared) / (n cubed - n); values near +1 or -1 indicate strong positive or negative correlation.

Chi-squared test compares observed and expected frequencies: chi-squared = sum of (O - E) squared / E; degrees of freedom = (rows - 1)(columns - 1).

Mann-Whitney U test compares two independent samples; a low U value indicates a significant difference between groups at a chosen significance level.

Fieldwork design: state hypothesis, choose sampling strategy, record data with units, repeat for reliability, control variables, and consider risk assessment and ethics.

Map skills: grid references (four-figure for area, six-figure for precise location), scale calculations (distance = map distance x scale), contour interpretation and cross-sections.

GIS layers combine spatial data (e.g. land use, flood risk, population density) for overlay analysis; choropleth maps show density, isoline maps show continuous values.