Topographical Maps, Atmosphere, Weather & Weathering
1. Representation of Geographical Features (Topographical Maps)
What Is a Topographical Map?
A DETAILED map showing natural features (hills, rivers, forests) and human-made features (roads, railways, settlements, canals) — using CONVENTIONAL SYMBOLS and COLOURS.
Scale
Three ways to show scale:
- Statement Scale: 1 cm = 1 km
- Representative Fraction (RF) : 1:100,000
- Linear/Graphic Scale: A drawn line divided into units
Colours on Topo Maps
| Colour | What It Represents |
|---|---|
| Blue | Water — rivers, lakes, canals |
| Green | Forests and vegetation |
| Brown | Contour lines |
| Red | Roads, settlements, grid lines |
| Yellow | Cultivated land |
| Black | Railway lines, boundaries, names |
Contour Lines
Lines joining points of EQUAL HEIGHT above sea level.
- Closely spaced contours: STEEP slope
- Widely spaced contours: GENTLE slope
- Concentric, closed contours: HILL or MOUNTAIN
- Concentric contours with INWARD ticks: DEPRESSION
2. The Atmosphere
Layers of the Atmosphere (From Earth Upward)
| Layer | Key Feature |
|---|---|
| Troposphere (0–12 km) | WHERE WEATHER HAPPENS. Temperature DECREASES with height. |
| Stratosphere (12–50 km) | Contains OZONE LAYER (absorbs harmful UV radiation). Temperature INCREASES. |
| Mesosphere (50–80 km) | Meteors BURN UP here. Coldest layer. |
| Thermosphere (80–600 km) | AURORA. Radio waves reflected. |
Atmospheric Pressure
The WEIGHT of air pressing down on the Earth. Measured by a BAROMETER.
- HIGH pressure: Sinking air. Clear skies.
- LOW pressure: Rising air. Clouds, rain.
3. Weather and Climate
| Weather | Climate | |
|---|---|---|
| Time | SHORT-TERM (hour to hour, day to day) | LONG-TERM (average of 30+ years) |
| What it tells | What's happening RIGHT NOW |
Elements of Weather
- Temperature (thermometer — max/min)
- Humidity (wet/dry bulb thermometer, hygrometer)
- Rainfall (rain gauge)
- Wind (anemometer — speed; wind vane — direction)
- Atmospheric pressure (barometer)
Types of Rainfall
| Type | Mechanism |
|---|---|
| Convectional | Sun heats surface → air rises → cools → condensation → heavy SHOWERS. Equatorial regions. |
| Orographic (Relief) | Moist air FORCED UP a mountain → cools → rains on WINDWARD side. Leeward side = DRY (Rain Shadow). |
| Cyclonic (Frontal) | Warm air RISES over cold air along a FRONT. Widespread, long-duration. Temperate regions. |
4. Weathering and Soil Formation
What Is Weathering?
The BREAKING DOWN of rocks IN SITU (in place — without movement). 'Weathering PREPARES the material. Erosion MOVES IT.'
Types of Weathering
| Type | Mechanism | Examples |
|---|---|---|
| Physical (Mechanical) | Rocks break WITHOUT chemical change | Frost action (freeze-thaw), heating/cooling, exfoliation (peeling layers) |
| Chemical | Rocks DECOMPOSE — chemical composition CHANGES | Oxidation (rusting), carbonation (limestone dissolved by CO₂ in rainwater), hydration |
| Biological | Living organisms break rocks | Tree roots. Lichens and mosses (produce acids). Burrowing animals. |
Soil Formation (Pedogenesis)
Soil = WEATHERED ROCK + ORGANIC MATTER (humus) + WATER + AIR. Factors: parent rock, climate, vegetation, topography, TIME. Soil takes HUNDREDS of years to form a few centimetres — it is a PRECIOUS, renewable-but-slow resource.
