Knowledge Organiser: Map Skills
Map Types
- Topographic (OS): symbols, contours, scale — physical + human features
- Choropleth: shaded areas — weakness: hides internal variation
- Isoline: equal-value lines (isobars, isotherms)
- Dot map: distribution pattern — weakness: no exact figures
- Proportional symbol: size = value — weakness: hard to compare circles
- Flow line: arrows showing movement and volume
OS Map Rules
- 1:50,000 → 2 cm = 1 km (Landranger, pink)
- 1:25,000 → 4 cm = 1 km (Explorer, orange)
- Contours every 10 m (1:50,000); every 5 m (1:25,000)
- Close contours = steep; wide contours = gentle
- V-shapes pointing uphill = river valley
- Concentric rings = hill summit
- Index contour = every 50 m (thicker + labelled)
Grid References
- Rule: easting then northing — "along the corridor, then up the stairs"
- 4-figure = 1 km² square (e.g., 4210)
- 6-figure = 100 m² point (e.g., 423104)
- CARTS: Corridor, Always, Room, Tenths, Six
- Tenths: divide each km square into 10 equal strips
- Check: first two digits of 6-figure = easting of 4-figure
Bearings and Coordinates
- N = 000°, E = 090°, S = 180°, W = 270°
- NE = 045°, SE = 135°, SW = 225°, NW = 315°
- Measured clockwise from north, always 3 figures
- Latitude = horizontal (flat) — given FIRST
- Longitude = vertical (long pole-to-pole) — given SECOND
- London: 51°N, 0°W | Nairobi: 1°S, 37°E | Sydney: 34°S, 151°E
Common Mistakes
- Reversing grid reference order: Always go along the easting FIRST, then up the northing — "along the corridor, then up the stairs"; reversing gives a completely different location on the map
- Giving a 4-figure reference when a 6-figure is needed: A 4-figure reference identifies a 1 km² square; a 6-figure reference pinpoints a 100 m² location — read the question carefully to give the right level of precision
- Misreading contour intervals: On a 1:50,000 OS map, contours are every 10 m; on a 1:25,000 map, every 5 m — check the map scale before estimating height or gradient
- Confusing latitude and longitude: Latitude lines are horizontal and measure distance from the equator (given first); longitude lines are vertical and measure distance from the Prime Meridian (given second) — remember "lat is flat"
Memory Aid
- 1:50,000 map → 2 cm = 1 km
- 1:25,000 map → 4 cm = 1 km
- Choropleth: hides variation WITHIN each shaded area
- Dot map: cannot give exact figures
- Proportional symbols: hard to compare circle sizes precisely
- Isoline: difficult to read values between lines