Lesson Notes By Weeks and Term - Senior Secondary 3

Map reading

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TERM – 2ND TERM

WEEEK SIX

Class: Senior Secondary School 3

Age: 17 years

Duration: 40 minutes of 5 periods each

Date:

Subject: Geography

Topic: MAP READING

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

  1. Calculate the gradients and vertical exaggeration
  2. Explain the procedures for drawing cross section /profile;
  3. Interpret cross section/profile to determine indivisibility of places on topographical maps

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers,

demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S

ACTIVITY

STEP 1

INTRODUCTION

The teacher introduces gradients and vertical exaggeration and give formulas for calculating them.

Teacher aid students to carry out calculations

Students in small groups calculate the gradients and vertical exaggeration.

STEP 2

EXPLANATION

Teacher discusses the procedures for drawing cross section /profile;

Students in group describe the procedures for drawing cross section/profile

STEP 3

DEMONSTRATIO

N

Teacher show students how to interpret cross section/profile to determine indivisibility of places on topographical maps

 Individual students, draws a cross section/profile of any two points and interpret cross section/profile to determine indivisibility of places on topographical maps

STEP 4

NOTE TAKING

The teacher writes a summarized note on the board

The students

copy the note in

their books

 

NOTE

MAP READING

Calculating gradients and vertical exaggeration

Gradients

Gradients refer to the slope or incline of the terrain. It indicates the rate of change in elevation over a certain distance on a map. Gradients are commonly expressed as a ratio or percentage and help individuals understand the steepness of hills, mountains, or other features on the map.

To calculate gradients, the following specific procedures apply:

  1. Choose Two Points: Select two points on the map to calculate the gradient between them.
  2. Determine Elevation Difference: Find the difference in elevation between the two points. This is the vertical change.
  3. Measure Horizontal Distance: Measure the horizontal distance between the two points on the map.
  4. Calculate Gradient: Divide the vertical change (elevation difference) by the horizontal distance to obtain the gradient. It can be expressed as a ratio, percentage, or degrees.

Formula for calculating gradient.

Gradient = Difference in height (meters)

                   Horizontal distance (meters)

 

Vertical exaggeration

Vertical exaggeration is a factor by which vertical scale is increased or decreased relative to the horizontal scale. It is used to enhance the visibility of elevation differences, making subtle variations more noticeable.

For example, if the vertical exaggeration is set to 2:1, it means that the vertical scale is doubled compared to the horizontal scale. This can be useful in geological cross-sections or topographic profiles to emphasize terrain features like mountains or valleys that might be visually obscured with a realistic scale.

The procedure for calculating vertical exaggeration involves determining the ratio between the vertical and horizontal scales in a graphical representation.

1.Convert the verticalscale into a representative fraction (R.F) or a ratio

2.Write down the horizontal scale of the map also as ratio

3.Divide the horizontal scale by the vertical scale to get the vertical exaggeration.

 Formula for calculating exaggeration

Vertical exaggeration = Horizontal Scale

                                            Vertical Scale

Example 1. If the vertical scale of a map is 1cm to 100m (i.e. 1mm to 10m) while the map scale is 1:100,000. Calculate the vertical exaggeration.

Solution

The ratio of vertical scale = 1:10,000

Horizontal scale = 1:1)0,000

Vertical exaggeration = 100,000/10,000 = 10.0

Thus vertical exaggeration = 10.0

Procedures for drawing cross section /profile

Drawing a cross-section or profile involves creating a two-dimensional representation of the Earth's surface along a chosen line. This is particularly useful in geology, geography, and engineering for visualizing the topography and features along a specific transect. The following are the general procedures for drawing a cross-section:

Step1. Take a thin strip of paper and place it along the transect line on the map. Mark A at the start of the transect and B at the end.

Draw a line to connect the two points A and B as seen in the image below.

Step 2:  Use a ruler and pencil to draw the horizontal axis of the graph exactly the same length as the transect A-B.

Step 3: Place the strip of paper along the x-axis at the bottom of the graph. Line A and B up with the vertical axes.

Step 4: Plot the heights marked on the piece of paper onto the graph

Step 5: Use a pencil to connect the dots in the graph with a smooth line.

Interpreting cross section/profile to determine indivisibility of places on topographical maps

To determine the indivisibility of places on topographical maps using cross-sections or profiles, analyze the contour lines. If contour lines are closely spaced, indicating steep terrain, the place is likely indivisible.

 Conversely, widely spaced contours suggest gentle slopes and divisibility. The vertical exaggeration in profiles helps visualize elevation changes.

EVALUATION: 1. Differentiate between gradients and vertical exaggeration, given formulas.

  1. How do you interpret a cross section to determine indivisibility of places on a topographic map
  2. Work out the vertical exaggeration of a cross-section if the vertical scale is 1cm represents 50 metres, and the scale of the map is 1: 250,000.

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively