Geography glossary

Definitions are concise revision aids. A term must be interpreted in the context of the map, scale, date and method used by a source.

Map and spatial analysis

• Absolute location: Position expressed through a coordinate system such as latitude and longitude.
• Atlas: A collection of maps arranged by theme or region; always check its edition and legend.
• Cartographic generalisation: Selection and simplification of features so they remain legible at a given map scale.
• Contour: A line joining points of equal elevation above a stated vertical datum.
• Coordinate: A numerical reference locating a point in a defined grid or geographic system.
• Datum: The reference surface and framework used to calculate coordinates or heights.
• Geographic Information System (GIS): A system for storing, analysing and displaying spatially referenced data.
• Grid reference: A location identified using intersecting lines on a map grid.
• Isobar: A line joining points with equal atmospheric pressure at a stated time.
• Isotherm: A line joining places with the same temperature for a stated period.
• Latitude: Angular distance north or south of the Equator.
• Legend: The key explaining symbols, colours, units and classes on a map.
• Longitude: Angular distance east or west of the Prime Meridian.
• Map scale: Relationship between distance on a map and corresponding ground distance.
• Projection: Mathematical transformation of the curved Earth onto a flat surface; every projection distorts some properties.
• Remote sensing: Collection of information about an area from a distance, commonly by satellites or aircraft.
• Thematic map: Map emphasising one subject, such as rainfall, population density or crop distribution.
• Topographic map: Map showing relief and selected natural and human-made features with a defined scale and legend.

Earth structure and landforms

• Alluvium: Sediment deposited by flowing water, commonly in floodplains and deltas.
• Arcuate range: A mountain chain with a curved plan form, such as the Himalayan arc.
• Basin: Area drained by a river and its tributaries, bounded in part by drainage divides.
• Bhangar: Older alluvium forming relatively higher surfaces in parts of the Northern Plains; local usage and mapping vary.
• Bhabar: Coarse piedmont deposits along parts of the Himalayan foothills where streams may disappear into porous material.
• Biosphere: The parts of Earth where life exists, including linked terrestrial and aquatic ecosystems.
• Delta: Low depositional landform at a river mouth where a river commonly divides into distributaries.
• Drainage divide: High ground separating neighbouring river basins.
• Dune: Mound or ridge of sediment shaped mainly by wind; form and mobility depend on sediment and vegetation.
• Escarpment: Long, relatively steep slope separating surfaces of different elevation.
• Floodplain: Low land adjacent to a river, shaped by channel migration and overbank deposition.
• Geomorphology: Study of landforms and the processes that shape them.
• Geosyncline: Historical term used in older explanations of mountain building; modern geology describes plate convergence and crustal processes more precisely.
• Laterite: Soil or weathered material enriched in iron and aluminium under particular drainage and weathering conditions; not a single uniform soil type.
• Levee: Natural raised river-bank deposit or an engineered embankment; context distinguishes the two.
• Lithosphere: Earth's rigid outer shell, including crust and uppermost mantle, divided into moving plates.
• Loess: Wind-deposited silt; it is not a defining blanket over India's plains.
• Plate tectonics: Framework explaining movement and interaction of lithospheric plates.
• Regolith: Unconsolidated material overlying bedrock, including weathered rock and transported sediment.
• Relief: Variation in elevation and slope across a land surface.
• Talus: Angular rock fragments accumulated below a steep slope or cliff.
• Terai: Moist, marshy belt south of the Himalayan foothill deposits in parts of the northern region.
• Weathering: Breakdown or alteration of rock in place by physical, chemical or biological processes.

Drainage and water

• Antecedent drainage: River course that maintained its path while uplift or other landscape change occurred.
• Aquifer: Permeable geological formation that can store and transmit groundwater.
• Base flow: Portion of streamflow supplied relatively gradually, often by groundwater.
• Distributary: Channel branching away from a main river, common in deltaic settings.
• Estuary: Tidal river mouth where freshwater and seawater mix; not every coastal river forms one.
• Hydrograph: Graph showing change in river discharge or water level over time.
• Inland drainage: Drainage that does not reach the sea, often ending in a lake, marsh or arid basin.
• Perennial river: River with flow through most or all of the year, although discharge may vary greatly.
• River regime: Seasonal pattern of a river's flow or discharge.
• Tributary: Stream or river that joins a larger channel upstream.
• Watershed: Area draining to a common outlet; in practice the term may also refer to a smaller management unit.

Climate, soil and ecology

• Adiabatic cooling: Temperature decrease of rising air as it expands under lower pressure without exchanging heat with its surroundings.
• Anomaly: Difference between an observed value and a stated reference average; both place and period must match.
• Convection: Vertical movement of air or fluid driven by temperature-related density differences.
• El Niño: Periodic warming of central and eastern equatorial Pacific waters associated with changes in the coupled ocean-atmosphere system.
• Evapotranspiration: Combined water transfer to the atmosphere through evaporation and plant transpiration.
• Monsoon: Seasonal circulation reversal or marked seasonal shift in winds and rainfall, shaped by land, ocean and atmospheric processes.
• Orographic rainfall: Precipitation associated with moist air being forced to rise over elevated terrain.
• Rain shadow: Relatively drier area downwind of a mountain barrier under particular circulation conditions.
• Western Disturbance: Eastward-moving synoptic weather system that can bring winter precipitation to north-western India and adjoining regions.
• Black soil: Common name for clay-rich soils of several Deccan regions, often associated with basaltic parent material; properties vary by site.
• C-horizon: Weathered parent material beneath the main soil horizons.
• Laterisation: Weathering and leaching processes that may concentrate iron and aluminium under suitable conditions.
• Salinisation: Accumulation of soluble salts in soil to levels that can impair plant growth.
• Soil horizon: Distinct soil layer formed through processes such as addition, loss, transformation and movement of material.
• Watershed management: Coordinated management of land, water and vegetation in a drainage area to improve conservation and livelihoods.

Population, resources and economy

• Arithmetic density: Total population divided by total land area; it conceals internal distribution.
• Census: Systematic official count and description of a population at a defined reference time and under stated rules.
• Demographic transition: Model describing changing birth and death rates during social and economic change; actual paths differ.
• Forest cover: Canopy-based measure defined by the reporting agency's criteria; it is not identical to recorded forest area.
• Human Development Index (HDI): Composite indicator using health, education and income dimensions; it does not measure every aspect of well-being.
• Migration: Change of usual residence or movement for work, education, family or other purposes, measured under a specific definition.
• Population distribution: Spatial arrangement of people across an area.
• Population density: Population divided by a stated area; the chosen area and population date matter.
• Resource: Material, energy source or environmental service considered useful under particular technical, economic and social conditions.
• Tree cover: Tree patches outside or within larger forest areas, measured under the applicable inventory definition.
• Urban agglomeration: Statistically defined contiguous urban spread, including a core town and qualifying adjoining settlements under census rules.
• Yield: Output per unit of land or other input, calculated using aligned data definitions and periods.

Statistics and evidence

• Advance estimate: Preliminary estimate available before all final data and revisions are complete.
• Climatological normal: Average for a defined period and variable; a normal is not a forecast for a particular season.
• Confidence cone: Graphic around a forecast track indicating uncertainty under a product's definition; it is not a boundary of all possible impact.
• Denominator: Quantity by which a numerator is divided; a percentage is misleading if its denominator is unclear.
• Gross migration: Total inward and outward movements counted separately; it can be large even when net migration is small.
• Net migration: In-migration minus out-migration for a stated place and period.
• Provisional data: Data released subject to validation or revision.
• Reference period: Time interval to which an observation or estimate applies.
• Spatial resolution: Ground area represented by a pixel or unit in a spatial dataset; finer resolution does not alone guarantee accuracy.
• Statistical unit: Entity counted or measured, such as a person, farm, district, mine or crop year.

Exam-use reminder

For every map or statistic, record four things before drawing a conclusion: what is measured, where it applies, when it applies and how it was defined. If any one is missing, state the limitation rather than filling the gap with an assumption.