26 May 2020

Geography SS1

INTRODUCTION TO MAP READING (Contd)

Conversion from One Scale to Another

  1. Conversion from Statement Scale to R.F

Procedure :

  1. Write out the scale clearly
  2. Write out the two parts of the scale in the same unit; usually in the lower unit.
  • Write the scale as a fraction with the map measurement as the numerator, and the ground measurement as the denominator
  1. Divide through if need be before expressing the final answer as a ratio

Examples : Convert the following statement scales to R.F

  1. 1cm to 1km
  2. 2cm to 1km
  3. 1cm to 4km

Solutions:

  1. a) 1cm to 1km

Convert 1km to cm by multiplying with 100,000

1cm to (1km × 100,000) = 1cm to 100,000 cm

Expressing as a fraction,

1cm to 100,000cm = 1cm/100,000cm  

Expressing as a ratio / R. F

1cm to 1km is therefore 1:100,000 in R. F

  1. b) 2cm to 1km

2cm to (1km × 100,000) = 2cm to 100,000cm

Expressing as a fraction and dividing through

2cm / 100,000cm = 1/50,000

Therefore 2cm to 1km is 1:50,000 in R. F

Note: 2cm to 1km may also be written as 1cm to ½km

  1. c) 1cm to 4km

Now try to do this on your own, following the steps shown in the worked examples above.

  1. Conversion from R. F to statement scale

Procedure :

  1. Write out the scale clearly
  2. Divide the ground measurement on the right hand side of the ratio by 100,000 to convert to km

Examples: Convert the following R. F scales to statement scales

  1. 1:50,000
  2. 1:150,000
  3. 1:20,000

Solutions :

  1. 1:50,000

Divide the ground measurement by 100,000

Hence, 50,000/100,000 = ½km

Therefore 1:500,000 = 1cm to ½km or 2cm to 1km in statement scale

  1. 1:150,000

Dividing ground measurement by 100,000

150,000/100,000 = 1cm to 3/2km or 2cm to 3km in statements scale

  1. 1:150,000

Again try the last one on your own

  1. Conversion from Linear Scale to Statement or R. F Scale

Procedure :

  1. Use ruler to measure the length of only one unit on the linear scale, starting from 0 to the next figure which could be 1,2 or 3 as the case may be. While doing this, make sure the zero on the ruler aligns with the zero on the linear scale
  2. The length measured with the metre rule represents the map part of the scale in centimeter, while the first value on the linear scale represents the ground equivalent in kilometer.

For instance, the linear scale below can be interpreted as 1cm to 1km in statement scale or 1:100,000 in R. F

 

Size of a Scale

A scale may either be small or large.

  1. Small Scale Map: shows a large area but with little detail and only important features are shown. Small scales always have large denominators. Examples, 1:1000,000 ; 1:2000,000; 1:250,000
  2. Large Scale Map: shows small area but with more details. Large scales always have small denominators. Examples, 1:5000; 1:250; 1:20

Note: the larger the denominator, the smaller the scale; the smaller the denominator, the larger the scale.

Now try arranging the following scales in ascending order:

1:50,000, 1:200,000, 1:200, 1:3,000,000, 1:500,000

 

Download Document Here  Geography SS1

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