Key Terms

📖 Key Terms

OS map (Ordnance Survey map) — A detailed, accurate topographic map of the UK showing both physical and human features using standardised symbols and a precise scale. The two GCSE scales are 1:25,000 (Explorer, 1 cm = 250 m) and 1:50,000 (Landranger, 1 cm = 500 m). Maps use grid lines, contours and a key to encode location, relief and land use.

Grid reference — A code used to identify a location on an OS map. A 4-figure grid reference (e.g., 4210) identifies a 1 km² square — not a precise point. A 6-figure grid reference (e.g., 423104) locates a point within a 100 m × 100 m area by subdividing each km square into tenths. Rule: always give easting before northing — "along the corridor, then up the stairs."

Scale — The ratio between distance on the map and real-world distance. 1:50,000 means 1 cm on map = 500 m in reality (50,000 cm). Larger scale = smaller ratio number = more detail = smaller area covered. Smaller scale = larger ratio number = less detail = larger area covered.

Contour line — A line on a map connecting all points at the same height (altitude) above sea level. On 1:50,000 maps, contours are drawn at 10 m intervals; every 50 m is an index contour (thicker, labelled). Spacing indicates gradient: closely spaced = steep slope; widely spaced = gentle slope. Contours never cross and always form closed loops if followed far enough.

Relief — The shape of the landscape — its height, slopes, valleys, and ridges. Relief is encoded on OS maps using contour lines, spot heights, and triangulation pillars. When describing relief in an exam answer, always use specific contour values and mention the spacing pattern (close/wide) to demonstrate gradient.

Bearing — A direction expressed as a 3-figure number from 000° to 360°, measured clockwise from north. North = 000°, East = 090°, South = 180°, West = 270°. Always written with three digits (not just 90° — always 090°). Used for precise navigation and for describing the direction from one feature to another on a map.

Latitude — Horizontal coordinate lines (parallels) measured in degrees north or south of the equator (0°). Range: 90°N (North Pole) to 90°S (South Pole). The UK lies between approximately 50°N and 61°N. Latitude is always given BEFORE longitude when writing a coordinate pair. Memory aid: lat = flat = horizontal.

Longitude — Vertical coordinate lines (meridians) measured in degrees east or west of the Prime Meridian (0°), which passes through Greenwich, London. Range: 0° to 180°E or 180°W. The UK lies between approximately 2°E and 8°W. Longitude is given AFTER latitude in a coordinate pair.

Choropleth map — A thematic map where areas are shaded according to a data value — typically darker = higher. Used for showing spatial patterns in statistical data (e.g., population density, GDP, rainfall). Key weakness: hides variation within each shaded area and implies sharp differences at boundaries where in reality the change may be gradual.

Isoline map — A map showing lines connecting points of equal value (not just height — any continuous variable). Contour lines are a specific type of isoline. Weather maps use isolines for pressure (isobars) and temperature (isotherms). Reading: areas between isolines have values between the adjacent line values.

Spot height — A dot with a number on an OS map giving the exact altitude at that precise point above sea level. Unlike contour lines (which give height along a whole line), a spot height gives the exact elevation at one specific location. Triangulation pillars (△) mark the most accurately surveyed high points.

Index contour — Every fifth contour line on an OS map, drawn thicker and labelled with its height value. On a 1:50,000 map, index contours appear every 50 m. They help you count up contour values quickly without reading every single line.