WBCHSE HS Geography key terms

The theory that Earth's lithosphere is divided into large rigid plates that move slowly over the weaker asthenosphere, and that their convergence, divergence and lateral sliding explain earthquakes, volcanoes, mountain building and ocean-basin formation.

The in-situ breakdown and alteration of rocks and minerals at or near Earth's surface by physical, chemical and biological processes, producing regolith and dissolved substances without transporting the material away.

The downslope movement of soil, regolith and rock under the direct influence of gravity, ranging from slow creep to rapid landslides and rockfalls, often triggered when slopes are steep, wet or undercut.

The lowest elevation to which a stream can erode its channel, commonly sea level but locally fixed by a lake, resistant rock bar or reservoir; it controls the lower limit of fluvial downcutting.

A landscape developed on soluble rocks such as limestone, dolomite and gypsum, characterised by solution hollows, caves, sinkholes, disappearing streams and underground drainage rather than a dense surface stream network.

The amount of incoming solar radiation reaching a given horizontal area at the top of Earth's atmosphere or at the surface, varying with latitude, season, time of day and atmospheric transparency.

The proportion of incident solar radiation reflected back to space by a surface or by the Earth-atmosphere system, expressed as a percentage or fraction; bright surfaces such as snow have high albedo.

An atmospheric layer in which temperature increases with height instead of decreasing, commonly forming on clear calm nights near the ground or aloft; it suppresses vertical mixing and can trap pollutants.

An apparent force caused by Earth's rotation that deflects moving air and water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, with strength increasing with latitude and wind speed.

A narrow, fast-moving band of strong upper-tropospheric westerly wind, often thousands of kilometres long, that steers surface weather systems and influences the timing and strength of the Indian monsoon.

A seasonal reversal of prevailing wind direction, most famously over South Asia, where moist south-westerly summer winds bring heavy rain and dry north-easterly winter winds dominate, driven by differential heating and pressure shifts.

The total concentration of dissolved salts in seawater, usually expressed in parts per thousand or practical salinity units; it varies with evaporation, precipitation, river inflow, ice formation and mixing.

A slow, global-scale overturning circulation of the ocean driven by differences in water density caused by temperature and salinity, linking surface and deep waters and redistributing heat around the planet.

The periodic rise and fall of sea level at a place, caused mainly by the gravitational attraction of the Moon and Sun and by centrifugal effects, with spring and neap variations through the lunar month.

The upward movement of cold, nutrient-rich water from depth to the ocean surface, often caused by offshore winds or diverging currents; it supports high plankton productivity and rich fisheries.

A large regional ecological unit defined by its dominant climate, vegetation and associated animal life, such as tropical rainforest, savanna, desert, temperate grassland or tundra, recognised at a broad scale.

The gradual, directional change in species composition and community structure at a site over time, from pioneer colonisers to a more stable climax community, driven by interactions between organisms and environment.

A region with exceptionally high numbers of endemic species that has already lost a large proportion of its original natural vegetation, making it a priority for conservation; examples include the Western Ghats and Himalaya.

A salt-tolerant forest community growing in tropical and subtropical intertidal zones, with specialised roots and propagules; it stabilises mudflats, buffers coasts against storms and provides nursery habitat.

The number of people living per unit area, usually persons per square kilometre, calculated by dividing total population by total land area; it reveals uneven distribution but not crowding or resource pressure by itself.

The number of females per 1,000 males in a population, or sometimes males per 100 females; in Indian census usage it is females per 1,000 males and reflects social and demographic conditions.

The average number of children a woman would bear during her reproductive lifetime if current age-specific birth rates remained constant; a summary measure of the level of childbearing in a population.

The ratio of the population outside the working-age range, usually children below 15 and older persons above 64, to the working-age population, expressed per 100 persons aged 15-64.

The increasing proportion of a country's or region's population living in towns and cities, accompanied by the growth of urban areas and changes in economy, land use and service demand.

Any element of the physical or human environment that people value and can use to satisfy needs or wants, given available technology and economic conditions; such elements are culturally defined and change over time.

A manufacturing activity that can locate almost anywhere because it is relatively unaffected by weight, bulk or perishability of raw materials and products, and depends more on labour, capital, markets or policy incentives.

A place where goods are transferred from one mode of transport to another, often requiring unpacking or repacking, so that transfer and handling costs make it a favoured location for processing or manufacturing.

A designated area within a country where business and trade laws differ from the rest of the country, typically offering tax incentives, simplified procedures and infrastructure to attract export-oriented investment and industry.

A reddish, iron- and aluminium-rich soil formed in hot humid tropical areas by intense leaching of silica and bases; it is often acidic, low in fertility and hardens on exposure, common in parts of peninsular India.

The extensive mangrove-dominated delta region at the mouth of the Ganga-Brahmaputra system, shared by India and Bangladesh; it is a UNESCO World Heritage area, cyclone-prone and famous for tigers and coastal protection.

A multipurpose river-valley authority established in 1948 for the Damodar basin, modelled partly on the Tennessee Valley Authority, undertaking flood control, irrigation, hydropower, navigation and industrial development across Jharkhand and West Bengal.

A potentially damaging physical event, phenomenon or human activity that may cause loss of life, injury, property damage or environmental disruption; a hazard becomes a disaster only when it affects vulnerable people or assets.

The conditions, such as exposure, fragile livelihoods, poor housing and weak institutions, that make people or places susceptible to harm from a hazard; it is a key determinant of whether a hazard becomes a disaster.

The likelihood of harmful consequences, including deaths, damage and disruption, resulting from the interaction of hazards with exposed and vulnerable elements; it can be reduced through preparedness, mitigation and adaptation.

A formal process of predicting and evaluating the likely environmental effects of a proposed project or policy before approval, and of proposing measures to avoid, reduce or compensate adverse impacts.

The relationship between a distance measured on a map and the corresponding distance on the ground, expressed as a representative fraction, a verbal statement or a graphic bar.

A line on a map joining points of equal elevation above a datum, usually mean sea level; the spacing and shape of contours show slope steepness, valleys, ridges and other landforms.

The acquisition of information about Earth's surface and atmosphere from a distance, using sensors on aircraft or satellites that record reflected or emitted electromagnetic radiation, without direct physical contact.

A computer-based system for capturing, storing, managing, analysing and displaying geographically referenced data, allowing spatial queries, overlay and mapping to support planning and decision-making.

A large-scale, detailed map, usually prepared by a national survey organisation, showing relief, drainage, settlements, transport, land use and boundaries on a standard sheet line system with grid references.