CALCULATIONS
1. Distance
1.1 Measure using a paper strip, dividers or piece of string
1.2 Confirm the map scale
1.3 Formula: Distance = Map distance X Scale / 100 000
1.4 Units: The result is distance in km
2. Area
2.1 Measure length and breadth of block on the map
2.2 Confirm the map scale
2.3 Formula: A = l x b
2.4 Calculate:
(a) length (See 1 above)
(b) breadth (See 1 above)
2.5 Apply formula
2.6 Units: Answer is in km2 (square km)
3. Gradient (Steepness of slope / ratio between vertical height and equivalent distance)
3.1 Measure: Horizontal distance and record heights
3.2 Confirm the map scale and contour intervals
3.3 Formula: G = VI (Height) / HE (Distance)
3.4 Calculate:
(a) VI by subtracting lower height from higher (answer in metres)
(b) Distance (See 1 above)
3.5 Convert the answer to metres (Multiply by 1000)
3.6 Apply formula and simplify to 1: x form
3.7 Units: No units – it is a ratio
4. Vertical exaggeration
4.1 Purpose: To show relief clearly
4.2 Measure: Draw accurate cross section
4.3 Confirm: Map scale
4.4 Formula: VE = VS (Vertical scale)/ HS (Horizontal scale)
4.5 Calculate: VS by converting to common units
4.6 Convert: VS to a ratio scale
4.7 Apply formula – “tip and times”
4.8 Units: No units – answer is the times vertical has been exaggerated
5. Magnetic declination
5.1 Purpose: Shows difference between compass North and true North
5.2 Confirm:
(a) Mean magnetic declination in degrees and minutes
(b) Direction of declination
(c) Year of map
(d) Mean annual change
(e) Direction of annual average change
(f) Year of calculation
5.3 Calculate:
(a) Current year – map year = (A)
(b) Mean annual change X A = B
(c) If B is east subtract; if west add to or from Mean declination
5.4 Units: Degrees and minutes W or E
6. Geographic bearing (from point A to point B)
6.1 Draw line due north from point A
6.2 Draw line from Point A to point B
6.3 Use protractor to measure angle in clockwise direction from North 00 to point B
6.4 Bearing is in 3 digits degrees e.g., 043deg or 192deg
7. Magnetic bearing
7.1 Formula: Mag bearing = geog bearing + magnetic declination
8. Stream flow
8.1 Formula: Flow = Velocity (m/s) x Stream width (m) x Mean stream depth (m)
8.2 Units: Cubic metres per second (m3/ s OR cu. m. sec)
Checklist – Mapwork kit
• Ruler
• Pencil
• Dividers
• Protractor
• String
• Calculator
• Coloured pencils
• Sharpener
• Eraser
• Magnetic compass (will be supplied)
• Magnifying glass (optional)