Geography

Description of Relief

What is Relief?

  • Relief refers to the shape of the land, including its height and steepness.

  • Earth's land surface is uneven, consisting of hilly areas and low-lying regions.

  • Relief can be visually represented using maps or cross sections.

2.1 Showing Relief on a Map

Methods to Illustrate Highland and Lowland Areas

  1. Colouring:

    • Different colors represent highland (brown) and lowland (green) areas.

    • Color differentiation provides a rough idea of land height at a glance.

    • Example: A relief map of Hong Kong (Figure 1).

    • Key locations include New Territories, Kowloon, Lantau Island, and Hong Kong Island.

    • Height of land (in meters):

      • Peaks: 600 m

      • Elevations decrease to 0 m as it nears the river.

  2. Contouring:

    • Utilizes contour lines to indicate equal heights.

    • Example: A contour line at 40 m height.

    • Vertical Interval (V.I.): The height difference between two consecutive contour lines, e.g., V.I. = 20 m (40 m - 20 m).

    • Questions:

      • Are locations C, D, and E at the same height? What is their height?

      • Estimate the heights of regions A and B.

      • Does the height of land along D-E vary?

  3. Conventional Signs:

    • Uses conventional trigonometric signs for specific heights (⚫ / +).

    • Example: Heights at trigonometric stations.

2.2 Showing Relief on a Cross Section

  • Concept: Imagining a hill cut vertically reveals a cross section, depicting the hill's shape.

  • Drawing a cross section from a contour map involves selecting a line, and plotting height changes on a graph (Figures 4a and 4b).

Steps to Draw a Cross Section

  1. Draw a Line: From point A to B on the map.

  2. Paper Strip Method:

    • Mark points A and B on the strip, including their heights.

    • Note contour heights and features intersected by A-B; label as ups (A) or downs (V).

  3. Frame Drawing:

    • Create a frame proportional to A-B’s length; use a vertical scale for height representation.

    • Example vertical scale: 1 cm = 200 m.

  4. Height Marking: Translate contour heights to the vertical frame.

  5. Drawing the Curve: Connect the heights smoothly.

    • Adjust based on ups or downs between equal heights.

  6. Annotate: Mark features and give the cross section a title to enhance clarity.

    • Optionally, shade the cross section for visual clarity.

Calculating Vertical Exaggeration (V.E.)

  • Purpose: To emphasize land shapes by adjusting the vertical scale relative to the horizontal map scale.

  • Formula for V.E.:
    V.E. = \frac{Vertical scale}{Horizontal scale}

  • Example Calculation: If vertical scale is 1 cm to 100 m and horizontal scale is 1 cm to 200 m:

    • V.E. = \frac{1:100}{1:200} = 2

    • Meaning the vertical exaggeration is 2 times.

2.3 Describing the Steepness of a Slope

A. Study the Spacing of Contour Lines

  • Wide apart contour lines indicate gentle slopes.

  • Close together contour lines indicate steep slopes.

  • Figures demonstrate these differences:

    • Gentle slope (Figure 9): Widely spaced contour lines.

    • Steep slope (Figure 10): Contour lines tightly packed.

B. Calculating Slope Gradient

  • Definition: Slope gradient quantifies steepness as the ratio of vertical distance to horizontal distance.

  • Illustrative example shows a slope with a 1:10 gradient.

    • This implies that for every 10 units horizontally, there is a 1 unit vertical rise.

  • Gradient Calculation Steps:

    1. Determine the vertical distance (difference in height).

    2. Measure the horizontal distance (ground distance).

    3. Calculate gradient using:
      Gradient = \frac{Vertical\, distance}{Horizontal\, distance}

2.4 Relief Features on Contour Maps

  • Identifiable Features:

    • Concave/Convex Slopes: Represented by the closeness of contour lines.

    • Valleys: Contours bend towards lower ground; often depicted between higher elevations.

    • Spurs: Contours bend towards higher ground; shown extending from hilltops.

    • Cliffs: Indicated by very closely packed contour lines across short distances, suggesting abrupt changes in height.

    • Ridged Terrain: Reflect the elevation changes across the landscape.

    • Plateaus and Basins: Represent larger flat areas at relatively constant elevation or lowland areas surrounded by higher ground.

    • Examples of these features are depicted in Figures 13-22.

2.5 Describing the Relief of Hong Kong

  • Key Features:

    • Predominantly steep hills with some lowland areas, concentrated in river valleys and coastal plains.

    • The highest peak: Tai Mo Shan, at an elevation of 957 meters.

    • Yuen Long Plain: The largest observed low elevation area within Hong Kong.

    • Major cities and towns are often built on reclaimed land surrounding embankments, such as those in Victoria Harbour.

    • Offshore islands contribute to Hong Kong’s geographical diversity and coastline.

  • Questions for Understanding:

    1. Which part of the New Territories is more hilly, the eastern or western side?

    2. Is Hong Kong International Airport located on reclaimed land? How can this be determined?

Vocabulary

  • Relief of Hong Kong: The arrangement of landforms within Hong Kong, covering various elevations and slopes.

  • Contour Line: Lines drawn on maps connecting points of equal elevation.

  • Vertical Interval (V.I.): The difference in height between two contour lines.

  • Vertical Exaggeration (V.E.): The apparent increase in vertical scale used on map representations.

  • Valley: A low area between hills or mountains.

  • Ridge: A long, narrow hilltop or mountain range.

  • Slope Gradient: A ratio expressing steepness related to a slope's incline.