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WEEK 4
TOPIC: MAP REDUCTION AND ENLARGEMENT
CONTENT:
- Map Copying
- Map Reduction
- Map Enlargement
- Scale size
Sub-Topic 1: MAP COPYING
Map copying is the ability to reproduce a given map extract as it is initially. This can best be done with the use of GRID LINES.
Grid Lines are lines drawn vertically and horizontally on map extracts. The lines are used to enlarge or reduce the original map to a given size, and to determine the position of a place or feature accurately. The distance between grid lines must be the same.
The number of grid lines should be in two digits figure such as 10, 15, 20, 25 etc.
Vertical grid lines are numbered from west to east and it is called ‘easting’ because they increase towards the east. The horizontal grid lines are numbered from south to north and called ‘northing’ because they increase towards the north. The combination of eastings and northings produces a four figure or six figure grid lines.
In the use of grid lines, the easting is read first while the northing is read last. For example, the position of A in the above grid system is 8242 (Four-grid system) while the position of B is 815415 (six-grid system).
Sub-Topic 2: MAP REDUCTION
Map reduction is the making of a given map smaller than the original one. This can be determined by the scale of the map. When the scale of the new map to be drawn is larger than the original map extract it means reduction. E.g. A scale of 1:50,000 to 1:100,000
Steps to follow:
- Be certain that you are reducing the map
- Determine how many times the new map is to be reduced
- Measure the length and width of the original map
- Divide the original map into square of equal size using pencil
- Draw the length and width of the new map
- Produce the same square in the new map
- Transfer the features required into the new map from the old one.
NOTE: To get how many times you are to enlarge or reduce, divide the old scale by the new scale.
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