You know those times when you open your map and the wind catches it and you curse and then you open it again, only this time into a smaller square? (Even digital folk will remember this.)
Imagine if the wind didn’t catch and wrestle the paper itself, but changed the features on the map.
That is exactly what happens when we build a map of our surroundings using our senses of hearing and smell.
The nearby town doesn’t move any closer when the wind changes, but it can seem closer if we smell its smoke more strongly or hear its industry more clearly.
Many people are familiar with this general idea, but far fewer appreciate how these sounds and smells are drawing a picture not just of distances and big landmarks, likes rivers and factories, but much more subtle features too.
As we walk up a steep hill, we hear the river gurgling below us. Then the gradient shallows and the sounds stop, the river disappears off our sound map. Then the hill gets steeper again and it reappears. Next it disappears for a long period. Then the wind picks up and changes direction and you smell it again. An awareness of the wind direction, married to our senses of smell and hearing, can help make sense of the terrain around you, even in poor visibility.
The next time you climb out of river valley, try to notice how the river announces its presence by its smell and sound, but also how the gradient in the valley is being mapped for you by the sounds you hear too.
In the image below I’ve sketched with colours how the sound of a river changes, even on a still air day. You can imagine how these colours shift with any changes in wind strength and direction.
One of my favourite anecdotes that draws many of these ideas together, came from a student on a natural navigation course. She told me she could tell when it was going to snow in winter, because she could smell the Medway power station and it was northeast of her.
In one sentence we can see how an awareness of the sense of smell, wind direction and season form a richer a map than even the finest Ordnance Survey work.