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OR # Form 2 Geography Lessons on Map Work

In this lesson we are going to discuss the marginal information

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Marginal Information
Information contained in the area surrounding the map.
1. Map name e.g. Yimbo.
2. Sheet title e.g. East Africa
1:50000 (Kenya).
3. Grid system numbers
4. Latitudes and longitudes
5. Compass direction with grid, true and magnetic north.
6. Scales
7. Key
9. Map identification
• Map series
• Sheet number or sheet index
Map Scales
A scale is a ratio of a distance on a map to a corresponding distance on the ground.
Types of Scales
Statement scale –expressed in words e.g. 1cm represents 1km, 1cm to 1km.
Representative Fraction (RF)- expressed as a fraction or ratio e.g. 1/200,000 or 1:200,000.
Linear scale-shown by a line which is subdivided into smaller units.
Conversion of Scales
Statement scale into RF
1cm rep 1km to RF
Multiply the number of
kilometres by 100,000
(1km=100,000cm) i.e.
1×100000=100,000.
Statement scale is 1/100,000
or 1:100,000.
2cm rep 1km
Divide both sides by two to
get 1cm rep ½ kilometres.
Multiply ½ by 100,000 to get
50,000.
RF is 1/50,000 or 1:50,000.
RF to Statement Scale
Divide the denominator by
100,000.
Write the scale in statement
form.
Linear Scale to Statement
Scale
• Measure a unit distance off a linear scale e.g.
• The distance is 4-3=1km which is represented by 2cm.
• Use the methods in (1) and (2) above.
Q. Given that the ground distance is 200km while the
distance on map is 20cm calculate the scale.
Sizes of Scales
1. Small scales- show a large area of land on a small size of
paper.
They show limited details e.g.
1:250,000, 1:500,000,
1:1,000,000.
2. Medium scales- used to represent a relatively smaller
area on a given size of paper
e.g. 1:50,000, 1:100,000, 1:125,000.
3. Large scales - used to represent a small area of land on a given piece of paper.
They show a lot of details e.g. 1:2,500, 1:10,000, 1:25000
Arranging Scales in Order
Ascending Order-smallest to largest
Descending Order-largest to smallest
(1)1/500,000
(3)1:25,000
(4)1/10,000
(2)1cm rep 500m
Uses of Scales
1. Estimating distances on maps
2. Measuring distances accurately-use dividers and ruler, piece of string or thread
for curved distances or straight edge of paper.
E.g. calculate actual distance of a line 8.5cm long on a map using the following scales.
(i) 2cm rep 1km
(ii) 1:100,000
3. Calculation of areas - no. of full grid squares+ number of ½grid squares/2 or use of rectangles (l×b) or triangles
(½ b×h).

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