Map Reading
Reading Contour Lines on Topographic Maps
A contour line joins points of equal elevation. On its own that definition does little, but read as a set, contours describe the exact shape of the ground: where it rises, where it folds inward, and how steeply it falls away. The skill is turning that flat pattern back into three dimensions before you walk it.
Spacing tells you the slope
The single most useful habit is reading the gap between lines. Closely packed contours mean a steep face; widely spaced contours mean gentle ground. When lines merge into what looks like a solid band, the slope is near-vertical, a cliff or a cut bank. This is why a leg that looks short on the map can be slow on the ground: distance covered is horizontal, but the climb hides in the spacing.
Contour interval
Every map states its contour interval in the legend, the vertical distance between adjacent lines. Confirm it before you plan. The same map pattern means something very different at a 5 m interval than at a 20 m interval.
Index contours and counting height
On most topographic maps, every fifth contour is drawn heavier and labelled with its elevation. These index contours let you count height quickly without tracing every line. To find the elevation of a point between labels, identify the nearest index contour, then count intermediate lines up or down by the stated interval.
Landform shapes
A handful of recognisable shapes cover most terrain you will navigate.
- Spur: contours point downhill, away from high ground. A nose of land you can follow down or use as a handrail.
- Re-entrant: contours point uphill, into the slope. A small valley or gully, and a very common control location.
- Saddle: a low point between two summits, shown as an hourglass of contours. Often the natural crossing point of a ridge.
- Knoll: a small closed loop of contour, a distinct rise that makes a reliable checkpoint.
Reading the Canadian Shield
Across much of central and eastern Canada, terrain is a patchwork of low rock ridges, bog, and lakes rather than dramatic relief. Contours can be subtle, and a two-line knoll may be the clearest feature on a leg. In this kind of ground, small spurs and re-entrants do the navigational work, and water bodies often give you firmer position fixes than the contours themselves.
A quick worked example
| Pattern on the map | What it is on the ground |
|---|---|
| Lines close together | Steep slope |
| Lines far apart | Gentle slope or flat |
| V pointing uphill | Re-entrant / gully |
| V pointing downhill | Spur / ridge nose |
| Closed loop | Hill or knoll |
The goal is fluency: glancing at a section of map and seeing the slope, not the lines. That comes from repeatedly comparing what the contours predicted with what the ground actually did, leg after leg.