Assam ASSEB HSLC Elective Geography cheat sheet

Earth's interior layers by depth: crust (0–35 km continental, 5–10 km oceanic), mantle to 2,900 km, outer core (liquid, 2,900–5,150 km), inner core (solid, to 6,370 km).

Discontinuities: Mohorovičić (crust–mantle), Gutenberg (mantle–core), Lehmann (outer–inner core); seismic P-waves vanish in the outer core, proving it is liquid.

Igneous rocks: intrusive (granite, gabbro, dolerite) cool slowly and are coarse-grained; extrusive (basalt, rhyolite, pumice) cool fast and are fine-grained or glassy.

Sedimentary rocks form by compaction and cementation of sediments (sandstone, limestone, shale) and are the main store of fossils; metamorphic rocks form under heat and pressure (marble from limestone, slate from shale, gneiss from granite).

Rock cycle: weathering → erosion → deposition → lithification (sedimentary) → heat/pressure (metamorphic) → melting → cooling (igneous); no rock type is permanent.

Plate boundaries: divergent (mid-ocean ridge, rift valley), convergent (ocean–continent gives fold mountains and volcanic arcs; ocean–ocean gives island arcs and trenches), transform (faults, earthquakes).

Weathering types: physical (frost wedging, exfoliation, salt crystallisation), chemical (carbonation, oxidation, hydrolysis), biological (root wedging, burrowing); erosion differs by transport of material.

Fluvial landforms: V-shaped valley, gorge, waterfall, meander, ox-bow lake, floodplain, delta, alluvial fan; karst landforms (sinkhole, stalactite, stalagmite) form by carbonation in limestone.

Glacial and aeolian landforms: cirque, arête, horn, U-shaped valley, moraine, drumlin (glacial); barchan, seif dune, mushroom rock, loess (aeolian).

Dry air composition by volume: nitrogen ~78%, oxygen ~21%, argon ~0.93%, carbon dioxide ~0.04%; water vapour varies 0–4% and is the main variable greenhouse gas.

Atmospheric layers: troposphere (weather, lapse rate ~6.5 °C/km), stratosphere (ozone layer, temperature rises with height), mesosphere, thermosphere, exosphere.

Insolation controls: angle of the sun's rays, day length, transparency of atmosphere, and distance from the sun; the tropics receive the highest annual insolation.

Temperature controls: latitude, altitude, distance from sea, ocean currents, prevailing winds, cloud cover, aspect and vegetation; annual range is greatest in continental interiors.

Pressure belts: equatorial low (ITCZ), subtropical highs (~30°), subpolar lows (~60°), polar highs; pressure falls with altitude and rises with cold, dense air.

Coriolis effect deflects winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere; deflection is zero at the equator and maximum at the poles.

Planetary winds: trade winds (NE and SE), westerlies (SW and NW), polar easterlies; monsoons are seasonal reversals driven by differential heating and pressure shifts.

Local winds: land and sea breezes (diurnal), valley and mountain breezes, katabatic and anabatic winds, foehn (warm dry), chinook, loo.

Precipitation forms: convectional (equatorial afternoon thunderstorms), orographic (windward slopes, rain shadow on leeward), cyclonic/frontal; relative humidity reaches 100% at dew point.

Ocean currents are driven by prevailing winds, Coriolis force, differences in temperature, salinity and density, and the shape of coastlines; they are deflected by the Coriolis effect.

Warm currents flow from low to high latitudes (Gulf Stream, Kuroshio, North Atlantic Drift); cold currents flow from high to low latitudes (Labrador, Canary, Benguela, Humboldt).

Cold currents intensify coastal deserts (Namib with Benguela, Atacama with Humboldt) and promote fog; warm currents keep high-latitude ports ice-free (North Atlantic Drift).

Tides: spring tides occur at new and full moon when sun and moon align (maximum range); neap tides occur at quarter moons when they are at right angles (minimum range).

Tidal period: semidiurnal tides have two high and two low tides per tidal day (~24 h 50 min); diurnal tides have one each; tidal bore forms in funnel-shaped estuaries.

Water resources: only ~2.5% of global water is fresh, and most of that is locked in glaciers and groundwater; usable surface freshwater is a small fraction.

Groundwater terms: water table, aquifer, aquiclude, infiltration, percolation, recharge; over-extraction causes land subsidence and saltwater intrusion in coastal aquifers.

Water scarcity drivers: uneven rainfall distribution, seasonal concentration, pollution, population growth, irrigation demand; remedies include rainwater harvesting, watershed management, and drip irrigation.

Population density = total population ÷ area in square kilometres; arithmetic density differs from physiological density (population per unit of cultivable land).

Demographic transition stages: high stationary (high birth and death rates) → early expanding → late expanding → low stationary → declining; natural increase = birth rate − death rate.

Population pyramid shapes: broad-based (expansive, high fertility), bell-shaped (stationary), narrow-based (constrictive, ageing population); sex ratio and dependency ratio read from the pyramid.

Push factors of migration: unemployment, poverty, war, famine, natural disaster; pull factors: jobs, higher wages, education, health care, political stability.

Migration types: internal (rural–urban, seasonal, circular), international (voluntary and forced), refugee versus economic migrant; remittances are a major income source for origin regions.

Settlement patterns: compact/nucleated (fertile plains, defence, water source), dispersed (hilly terrain, scattered farmland), linear (along roads, rivers, coasts).

Urban land-use models: concentric zone, sector, multiple nuclei; functions include CBD, residential zones, industrial areas, and rural–urban fringe.

Site and situation: site refers to the local physical features of a settlement (river bend, hilltop, spring); situation refers to its regional position and accessibility.

Subsistence farming (shifting cultivation, intensive paddy) is labour-intensive for local consumption; commercial farming (plantation, ranching, dairy) is capital-intensive for the market.

Agriculture types by climate: wet paddy in monsoon lands, wheat in temperate grasslands, Mediterranean crops (olives, grapes) in winter-rain regions, nomadic herding in drylands.

Industrial location factors: raw material, power, market, labour, transport, capital, government policy; weight-losing industries (steel, cement) locate near raw materials.

Industry classification: primary (extraction), secondary (manufacturing), tertiary (services), quaternary (knowledge); heavy versus light industry; cottage and small-scale industry.

Iron and steel needs iron ore, coking coal, limestone, water, and transport; cotton textiles locate near cotton, power, labour, and markets.

Transport modes: road (flexible, door-to-door), rail (bulk and long distance), water (cheapest for heavy goods), air (fast, costly, high-value goods), pipeline (liquids and gases).

Transport nodes and networks: break-of-bulk points, transhipment, hinterland, port function; transport corridors stimulate industrial growth along them.

Trade terms: balance of trade, exports versus imports, special economic zones, and the role of transport cost in comparative advantage.

Assam lies between roughly 24°N–28°N and 89°E–96°E; the Brahmaputra valley, Barak valley, and the Karbi Anglong–Dima Hasao hills are its three physiographic divisions.

The Brahmaputra enters India in Arunachal Pradesh as the Siang, flows through Assam, and is called the Jamuna in its lower Assam course before entering Bangladesh.

Assam climate is humid subtropical monsoon: heavy summer rainfall (Cherrapunji/Mawsynram in the Khasi Hills record some of the world's highest), high humidity, and mild winters.

Assam's economy: tea (largest tea-growing region in India, both Brahmaputra and Barak valleys), oil and natural gas (Digboi, Naharkatiya, Moran), coal, plywood, and silk (muga, eri, pat).

Floods and erosion: the Brahmaputra's braided channels, high sediment load, and bank erosion (including Majuli island shrinkage) cause recurrent floods; earthquakes add risk.

North-East states: Arunachal Pradesh, Nagaland, Manipur, Mizoram, Tripura, Meghalaya, Assam, and Sikkim; the region shares international borders with Bhutan, China, Myanmar, and Bangladesh.

Physiography of the North-East: Eastern Himalaya, Patkai Bum, Naga Hills, Manipur Hills, Mizo Hills, Meghalaya plateau, and the Barak plain; the Siliguri Corridor links the region to the rest of India.

Biodiversity: Kaziranga (one-horned rhinoceros), Manas, Nameri, and Dibru-Saikhowa national parks; tropical evergreen and semi-evergreen forests on the hills.

Physiographic divisions: Himalayan mountains, Northern Plains (Indo-Gangetic-Brahmaputra), Peninsular Plateau, Thar Desert, Coastal Plains, and Islands (Andaman and Nicobar, Lakshadweep).

Himalayan ranges: Trans-Himalaya (Karakoram, Ladakh), Greater Himalaya (Himadri), Lesser Himalaya (Himachal), Shiwaliks; passes include Zoji La, Nathu La, and Bomdi La.

Indian monsoon: southwest monsoon (June–September) brings most rainfall; retreating monsoon (October–November) affects the Coromandel coast; winter rainfall in Punjab comes from western disturbances.

Rainfall pattern: high on windward Western Ghats and the north-east, low in the rain-shadow Deccan and western Rajasthan; Mawsynram and Cherrapunji record extreme totals.

Natural vegetation: tropical evergreen (Western Ghats, North-East), tropical deciduous (most of India), thorn forest (Rajasthan), mangrove (Sundarbans), alpine (Himalaya).

Soil types: alluvial (Indo-Gangetic plain, most fertile), black/regur (Deccan trap, cotton, moisture-retentive), red (crystalline rocks, iron-rich), laterite (heavy rain, leached), desert, mountain, and saline-alkaline soils.

Soil conservation: contour ploughing, terracing, strip cropping, shelter belts, check dams, and afforestation to check erosion and gully formation.

Rivers: Himalayan rivers are perennial (Indus, Ganga, Brahmaputra systems); peninsular rivers are seasonal (Godavari, Krishna, Kaveri, Narmada, Tapi); the Ganga–Brahmaputra delta is the world's largest.

Scale types: statement (1 cm = 1 km), representative fraction (1:50,000), and graphical/linear scale; RF is unit-free and remains valid if the map is enlarged or reduced.

Conversion: 1:50,000 means 1 cm on the map equals 50,000 cm = 500 m = 0.5 km on the ground; 1:25,000 is a larger scale than 1:50,000.

Large-scale maps show small areas in more detail; small-scale maps show large areas with less detail; topographic sheets are typically 1:50,000.

Grid references: eastings are read first (vertical grid lines), then northings (horizontal lines); a four-figure reference gives a 1 km square, a six-figure reference a 100 m square.

Contours join points of equal elevation; closely spaced contours indicate steep slopes, widely spaced indicate gentle slopes; V-shapes pointing upstream mark valleys.

Map symbols and colours: blue for water, green for vegetation, brown for contours and relief, black for cultural features; conventional signs are explained in the legend/key.

Direction and bearing: true north versus magnetic north (magnetic declination); bearings are measured clockwise from north in degrees.

Relief representation methods: contours, hachures, hill shading, spot heights, benchmarks, form lines, and layer tinting.

Cross-section and gradient: gradient = vertical difference (rise) ÷ horizontal distance (run); a cross-section plots elevation against distance along a straight line.