Map skills

On an atlas or globe, any place can be located by its latitude and longitude, measured in degrees (°).

• Latitude is how far north or south of the equator (0°) a place is, up to 90° at the poles. Lines of latitude run east to west.
• Longitude is how far east or west of the prime meridian (0°), which runs through Greenwich in London, a place is, up to 180°. Lines of longitude run from pole to pole.

Latitude is given first: London is about 51.5° N, 0.1° W.

OS maps have a grid of 1 km squares. Read eastings (along the bottom) before northings (up the side): along the corridor, and up the stairs.

Four-figure grid reference, for the square with the campsite:

1. Find the line on the left of the square: 22.
2. Find the line along the bottom of the square: 42.
3. Grid square 2242.

Six-figure grid reference, for the campsite itself:

1. Imagine the square divided into tenths.
2. It is 6 tenths east of line 22: 226.
3. It is 2 tenths north of line 42: 422.
4. Grid reference 226422.

Scale shows how much smaller the map is than real life. On a 1:25 000 map, 1 cm on the map is 25,000 cm (250 m) on the ground, so 4 cm is 1 km.

Straight-line distance: measure with a ruler or the edge of paper, then compare with the scale line. On the Porthwen map, the church to the lighthouse is about 2.8 km.

Curved distance, along a road or river: lay paper along the route, turning it at each bend and marking it, then measure the total against the scale. The Afon Wen flows about 2.8 km across the extract, from its northern edge to its mouth.

Direction: use the eight compass points. The lighthouse is south-east of the church.

• Contour lines join places of the same height. Close together means steep; far apart means gentle.
• Spot heights give the exact height of a point, in metres.

Gradient is how steep a slope is: the rise in height divided by the horizontal distance, both in the same units, often written as "1 in…".

Worked example, on the Porthwen map: from the spot height of 42 m on Mor Head, south to the cliff edge at sea level, is about 720 m.

• Rise: 42 m. Distance: 720 m.
• 720 ÷ 42 ≈ 17, so the gradient is about 1 in 17.

For every 17 m you walk, you climb or fall 1 m.

A distribution is how things are spread across a map. To describe one:

1. Give the general pattern: where most are, using compass directions and place names. Are they clustered, in a line or spread evenly?
2. Use data or map evidence: names, numbers and grid references.
3. Point out any exceptions (anomalies).

Example: "On the Porthwen map, tourist facilities cluster in two places: in Porthwen village, in the centre (the information centre and campsite), and on Mor Head in the south-east (the car park and viewpoint). The exception is the picnic site, alone in the north-west, in grid square 2043."

Describing is saying where; explaining is saying why.

• Ground photographs show a place from eye level.
• Aerial photographs are taken from the air: oblique ones at an angle, showing the sides of hills and buildings; vertical ones looking straight down, like a map.
• Satellite images cover large areas, and can show things such as forest loss or flooding over time.

To use a photo, describe the foreground, middle ground and background, and link features to the map.

A field sketch or sketch map is a simple drawing of the main features. Label it with names, and annotate it with explanations, such as "wave-cut notch: eroded by hydraulic action".