Read a slope from contour lines

A contour line joins points at the same elevation. Closely spaced lines show a steep slope. Wider spacing shows a gentler slope. The map represents a three-dimensional landform on a flat sheet.

Contour lines show height and interval. They can show the direction of a ridge, the shape of a valley, and a steepening climb. At the common Canadian scale of 1:50,000, two centimetres on the map represent one kilometre on the ground. Distance and relief can be read from the sheet. Current travel conditions can't.

Natural Resources Canada groups map features as relief, water, vegetation, transportation, culture, boundaries, and place names. Each category is a generalization at the chosen scale. A wooded area doesn't describe every metre inside it. A trail symbol doesn't establish the state of the tread.

Surface, water, vegetation, weather, maintenance, and recent use affect the crossing. These conditions can change by season, by week, or during the same day.

Before a trip, contour spacing can compare the sustained shape of two approaches. It can't establish which route will be easier that day. That judgment needs current local information and an honest assessment of the group.

During a trip, compare the map with the place. Check the direction of drainage, the slope underfoot, the expected landmarks, and the time the crossing is taking. A wet root or fallen tree doesn't make the map wrong. It's current information the map was never built to provide.

Contour spacing shows slope shape. Current conditions determine travel difficulty.