Cartography and Geographic Skills: Scale, Coordinates, Relief and GIS
The Cartography and Geographic Skills domain tests map reading, scale and coordinate work, relief interpretation and basic GIS concepts. Marks are usually lost through unit errors and through confusing grid north, true north and magnetic north.
Scale
- Scale is a ratio: 1:50,000 means 1 cm on the map equals 50,000 cm, or 500 m, on the ground.
- Large scale (1:10,000) covers a small area in great detail; small scale (1:1,000,000) covers a large area with little detail. "Large scale" refers to the size of the fraction, not the size of the area.
Coordinates and location
- Georgia lies roughly between 41°N and 43°35′N and between 40°E and 46°45′E; Tbilisi is near 41.7°N, 44.8°E.
- Read latitude first (N/S), then longitude (E/W). Georgia keeps UTC+4 all year with no daylight saving.
- Topographic mapping commonly uses UTM; Georgia spans zones 37N and 38N.
Relief on maps
- Contours join points of equal height and the interval is constant on a given map. Closely spaced contours mean a steep slope; V-shaped contours pointing uphill mark a valley.
- Gradient = vertical difference ÷ horizontal distance, given as a percentage or in m/km.
- Aspect matters in Georgia: north-facing slopes hold snow longer, south-facing slopes are drier.
GIS basics
Vector data are points, lines and polygons; raster data are grids of cells such as elevation models and satellite images. Overlaying layers answers questions such as where landslide risk coincides with settlements.
Worked example
Two points on a 1:25,000 map are 4.8 cm apart; their spot heights are 620 m and 800 m. Find the ground distance and the gradient. Reasoning: ground distance = 4.8 × 25,000 = 120,000 cm = 1,200 m. Vertical difference = 800 − 620 = 180 m. Gradient = 180 ÷ 1,200 = 0.15, i.e. 15% or 150 m per km. Show units at each step.
Traps that cost marks
- Forgetting to convert centimetres to kilometres (divide by 100,000).
- Reading longitude before latitude.
- Ignoring magnetic declination when converting a compass bearing to a grid bearing.
- Using map distance instead of ground distance in a gradient calculation.