Representation of Geographical Features Chapter Notes | Geography Class 7 ICSE PDF Download

 Introduction

Topographical Maps

• Topographic maps show detailed and accurate representations of natural and man-made features.
• Features include roads, railways, power lines, relief, rivers, and lakes.
• They represent the three-dimensional Earth in a two-dimensional format.
• Prepared by national mapping organizations, like the Survey of India for India.
• Drawn on large scales for detailed representation.

Use of Colours on Maps

• Colours help identify different natural and man-made features.
• Standard colour conventions are used globally for uniformity.
• Blue represents water bodies like streams, lakes, snow fields, and glaciers.
• Green indicates forests and vegetation.
• White shows areas with little or no vegetation.
• Brown is used for contour lines showing elevation and relief.
• Black represents man-made features like temples, place names, boundaries, settlements, roads, and railways.
• Red marks highways, major roads, and township/range/section information.
• Pink indicates urban areas.

Signs and Symbols Used on a Map

• Maps use signs and symbols to represent physical and cultural features due to limited space.
• Features include relief, drainage, vegetation, settlements, temples, villages, cities, roads, and wells.
• Conventional signs are standardized globally for clarity and legibility.
• Symbols are small, recognizable, and convey specific information.
• Symbols are divided into three types: point, line, and area symbols.
• Point symbols represent specific locations like buildings, cities, dipping tanks, or trigonometrical beacons using simple shapes.
• Line symbols show linear features like roads, rivers, power lines, and borders, with variations like colored, thick, bold, multiple, or dotted lines.

Point Symbols

• Point symbols show a specific place, location, or site.
• They use basic shapes for easy recognition, even when small.
• Examples include buildings, cities, dipping tanks, and trigonometrical beacons.

Line Symbols

• Line symbols represent linear features like roads, rivers, power lines, and borders.
• They vary by being colored, thick, bold, multiple, or dotted.

Physical Features

Area Symbols

• Moraine shown with a pattern of small shapes.
• Coral reef marked with a dotted pattern.
• Lake represented with a blue filled shape.
• Swamp shown with a pattern of small lines.
• Tidal flat marked with a specific pattern.
• Mangroves represented with a tree-like pattern.
• Relief: Contours, spot heights, trigonometrical beacons.
• Water: Lakes, rivers, waterholes, reservoirs.
• Vegetation: Cultivation, orchards, vineyards, forests, plantations, woodland.
• Political: Boundaries.

Scale of a Map

• Map scale shows the ratio of distance on the map to the actual distance on the ground.
• Scales are presented in miles and kilometers.

Types of  Map Scales

Three are three types of  map scales as described here: 
they are:

• Direct statement
• linear scale
• Representative fraction (ratio).

Direct Statement Scale

• Expressed in words, e.g., 1 cm represents 15 km.
• Means 1 cm on the map corresponds to 15 km in reality.
• Easiest and most common method to understand.
• Should not use "equals" (e.g., 1 cm = 15 km is incorrect; use "represents").

Linear Scale or Bar Scale

• Shown as a line with numbers indicating distances.
• Requires measuring the line to determine the represented distance.

Representative Fraction or Ratio Scale

• Expressed as a ratio, e.g., 1:1,500,000.
• Means 1 unit on the map represents 1,500,000 units in reality (e.g., 1 cm = 1,500,000 cm).
• Both sides of the ratio use the same unit of measurement.

Different Scale Maps

• Large-scale maps show small areas with great detail, e.g., topographic maps or city road maps.
• Small-scale maps show large areas with less detail, e.g., maps of continents or the world.

Measuring Distance

Three methods: 

• Direct distances
• Indirect distances
• Calculating actual distance using a scale.

Measuring Direct Distances

• Measure straight-line distance between two points using a ruler.
• Use the map scale to calculate actual distance.
• Example: If 10 cm on a map with a scale of 1 cm = 100 km, actual distance is 1,000 km.
• For a ratio scale of 1:10,000, 5 cm on the map equals 50,000 cm (0.5 km) in reality.

Measuring Indirect Distances

• Measure distance along a route (e.g., a road) using a string to follow the path’s shape.
• Mark the distance on the string and measure it against the map’s scale.
• Example: If string measures 15 cm and scale is 1 cm = 5 km, actual distance is 75 km.

Calculating Actual Distance Using a Scale

• Example: For a scale of 1:5,000, if map distance is 8 cm, actual distance is calculated.
• Calculation: 8 cm × 5,000 = 40,000 cm = 400 m.

Solution

• Scale is 1:5000, meaning 1 cm on the map represents 5000 cm in reality.
• Map distance to actual distance ratio is 1:5000.
• Given map distance is 8 cm.
• Let the actual distance be 'a' cm.
• Set up the ratio: 8:a = 1:5000.
• Invert the fraction: a/8 = 5000/1.
• Multiply both sides by 8: a = 8 × 5000.
• Calculate: a = 40000 cm.
• Convert to meters: 40000 cm ÷ 100 = 400 m.
• Actual distance is 400 m.

Points To Remember

• Maps are two-dimensional representations of the Earth’s surface.
• Scales are shown as statements, ratios, or linear scales.
• Maps are categorized as large-scale or small-scale based on their scale.
• Conventional signs and symbols convey information in limited map space.