Practical geography: cartography, survey, statistics, remote sensing/GIS and field work
Practical geography
This is the highest-scoring, most rule-bound part of the paper: scale, projections, surveying, statistical treatment of data, remote sensing/GIS and field-work method. Marks are lost on units and formulas, not on ideas.
Core rules
- Scale forms: statement, representative fraction, graphical. Unit conversion: 1 km = 100 000 cm; 1:50 000 means 1 cm = 0.5 km.
- Projections trade area, shape, direction and distance: Mercator preserves direction (navigation) but exaggerates high-latitude area; conical suits mid-latitude east–west countries; zenithal suits polar maps.
- Prismatic compass: fore and back bearings differ by 180°; closing error is distributed by Bowditch's rule. Plane table: radiation, intersection, traversing, resection (three-point problem).
- Statistics: mean, median, mode, quartile deviation, standard deviation, coefficient of variation, Karl Pearson's r, Spearman's rank correlation, moving average.
- Remote sensing: resolution (spatial, spectral, temporal, radiometric), bands (visible, NIR for vegetation, thermal for temperature); GIS stores layers with attributes and supports overlay and buffer analysis.
Worked example
On a 1:50 000 map, a road measures 4.2 cm; the same road measures 2.1 cm on a second map. Find both ground distances and the second scale. Reasoning: first map 1 cm = 0.5 km, so 4.2 × 0.5 = 2.1 km on the ground. On the second map 2.1 cm represents 2.1 km, so 1 cm = 1 km, giving an RF of 1:100 000. The ground distance is invariant; only the scale changes.
Traps that cost marks
Forgetting to convert cm to km; computing the median of grouped data without the class-interval formula; using r for ranked data instead of Spearman's rho; drawing scale without labelling units; confusing spectral with spatial resolution in satellite images.