Cartography, Map Reading and Surveying Techniques
Cartography and map reading test scale, symbols, grid references, contours, bearings and basic surveying. The aim is to extract measured information from a map and to choose a suitable field method.
Core rules and concepts
- Scale may be statement, representative fraction or graphical. A representative fraction is unitless: 1:50,000 means one unit on the map represents 50,000 of the same unit on the ground.
- Contours join points of equal elevation. Close contours mean steep slope; widely spaced contours mean gentle slope. A V pointing upstream marks a valley; a closed depression has hachures.
- Bearings are measured clockwise from north. Magnetic bearing differs from true bearing by magnetic declination.
- Chain or tape survey measures horizontal distances; prismatic compass survey measures bearings; plane-table survey maps detail directly in the field; levelling finds height differences.
Worked example
A map distance of 4 cm represents 1 km on the ground. Convert 1 km to centimetres: 1 km = 100,000 cm. Representative fraction = map distance ÷ ground distance = 4 ÷ 100,000 = 1:25,000. Reasoning: both sides must use the same unit before simplifying, and the final RF has no unit.
Traps that cost marks
- Writing an RF with units such as 1:25,000 cm.
- Forgetting that 1 km equals 100,000 cm.
- Reading a contour V as a ridge instead of a valley.
- Confusing magnetic north with grid north or true north.