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Practical Skills

Contour Lines, Grid References, and Scale

Ages 10–14 25 min read Intermediate

Contour lines are the secret language of topographic maps. They tell you what the ground looks like in three dimensions — hills, valleys, ridges, cliffs — all from a flat sheet of paper. Once you can read contour lines, the landscape jumps off the page.

Contour Lines

A contour line connects points of equal elevation. Think of it as slicing a mountain horizontally at regular intervals and drawing the outline of each slice.

Reading Contour Lines

  • Close together: Steep slope. The closer the lines, the steeper the terrain.
  • Far apart: Gentle slope or flat ground.
  • Concentric circles: A hill or peak. The smallest circle is the top.
  • V-shapes pointing uphill: A valley or stream.
  • V-shapes pointing downhill: A ridge or spur.

The contour interval (usually noted in the legend) tells you the elevation difference between lines. On a 1:25,000 map, the interval is typically 10 metres.

Grid References

Grid references let you describe any location on a map with precision.

4-Figure Grid Reference

Identifies a 1km × 1km square. Read along the bottom first (easting), then up the side (northing). Remember: "Along the corridor and up the stairs." Example: GR 4523.

6-Figure Grid Reference

Identifies a 100m × 100m square — precise enough to find a specific feature. Divide each grid square into 10 mentally. Example: GR 452234.

Measuring Distance

For straight-line distance: use a ruler and the scale bar. For route distance (along paths): use a piece of string laid along the route, then measure the string against the scale bar. On a 1:25,000 map, 4cm = 1 kilometre.

Estimating Walk Time

Naismith's Rule (1892, still used):

  • Allow 5 km/hour on flat ground
  • Add 1 minute for every 10 metres of ascent

A 10km walk with 500m of climbing would take approximately: 2 hours (flat) + 50 minutes (climbing) = 2 hours 50 minutes.

Tonight's Question

"If we were planning a bushwalk, how would we use contour lines to choose an easy route vs a challenging one?"

3D Contour Model

  1. Print or draw a simple contour map of a hill on cardboard.
  2. Cut out each contour line from cardboard.
  3. Stack them, largest at the bottom, to create a 3D model of the terrain.
  4. Compare the model to the flat map. Can you see how contour lines represent the shape?
  5. Practise giving grid references: hide a small object on the map and give each other the grid reference to find it.

Go Further

  • Practice: Download a free topographic map of a nearby national park and identify features using contour lines.
  • Research: What is LiDAR and how is it changing the way maps are made?
  • Book: Map Addict by Mike Parker (2009) — a love letter to maps and map reading.
  • Challenge: Give someone a 6-figure grid reference and see if they can find the exact spot on a map.

What We Simplified

  • Contour lines show elevation, not vegetation or surface. A steep slope could be bare rock or dense forest — contours alone don't tell you.
  • Naismith's Rule is approximate. Terrain type, fitness, weather, and load all affect walking speed significantly.
  • Digital elevation models are replacing contour lines. Modern mapping software uses continuous elevation data, but contour lines remain the standard on printed maps.

Sources

  • Geoscience Australia. "Understanding Topographic Maps." ga.gov.au
  • Parker, M. (2009). Map Addict. Collins.
  • Naismith, W.W. (1892). "Excursions." Scottish Mountaineering Club Journal, 2, 135.

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