Tech Tip #1 - Contour Lines

In my opinion contour lines (often referred to simply as contours) are the most useful feature on any map. Forests grow and are cut down, fences are built and knocked over, streams can dry up in the summer or appear from nowhere in the winter, but mountains tend to stay roughly the same shape for a fairly long time.

So what is a contour line? The technical definition is "a line joining points of equal elevation on a surface".

Basically, they're the little brown lines that tell you tell you how high in the sky you really are.

They do this at set intervals. On almost all Ordnance Survey maps the contour interval (the vertical distance between contour lines) is 10 metres (except things like specialist orienteering, or large scale tour maps) and Harveys maps use a 15m interval. Meaning if you walk from one contour line to the next you will have gone up, or down, 10 or 15 metres (depending on which map you're using).

What is important is that contours indicate vertical distance, not horizontal. So, if the contour lines are widely spaced (see A), you'll be walking a lot of horizontal and not much vertical, ie on a nice gentle slope, and if they are close together (see B) you'll be doing a lot of vertical and not much horizontal, you'll be on a steep slope (somewhere to steer clear of when you're traipsing round in the dark perhaps...?)

As mentioned above, contour lines join points of equal elevation, so if you were to walk along one you would not gain or lose any elevation. This is referred to as “contouring” (a.k.a walking around a hill).

The numbers inset into the contour line tell you the elevation (height above sea level, in metres) of everything along that line. In addition, the top of the number will always point up hill (ie if there really were giant numbers painted on the hillside you would have to stand at the bottom of the hill to read them).

So, contours show you the shape of the ground. Pretty useful.