Great Works: Ambleside (1786), Francis Towne

Paul Mellon Collection, Yale Centre for British Art, New Haven, Connecticut, US

Taking a line for a walk, that was Paul Klee's line. At the start of his Pedagogical Sketchbook he proposes "an active line on a walk, moving freely, without goal. A walk for a walk's sake. The mobility agent is a dot, shifting its position forward."

It's a lesson in how to draw without limits. Take up your pen, and wander. Make an unpredictable, meandering path across the paper. Be guided neither by the shapes of the world nor the rules of geometry. Simply go ahead, on any course, by impulse alone.

And it's possible. You can proceed like that. But the famous metaphor, though it sounds inviting, is also misleading. Going for a real walk, even a walk for a walk's own sake, is normally less free than Klee suggests. A pen can happily amble all over a sheet of paper, because a sheet of paper is smooth and flat. But the earth is not flat.

The surface of the world upon which we normally take our walks is a distinctly uneven terrain. It's not a piece of paper. It has hills and water and vegetation and human constructs, all kinds of blockage. It has established paths, too, and lines of least resistance, which may (over time) turn into paths. These are the conditions in which we do our walking. Even when we don't have any plans for where we're going, even in the most open country, the lie of the land steers our footsteps.

And taking a line for a walk, if it were really like walking, wouldn't be an act of pure freedom, "a dot, shifting its position forward." It would have to negotiate obstacles. It would follow known roads. Klee's metaphor forgets the real activity that's behind it.

All the same, it reflects the reality of its time. Pedagogical Sketchbook was put together in the early 1920s, when Klee was teaching at the Bauhaus, the now legendary German art school. This coincided with an active social movement, which had originated in the late 19th century, but got more organised after the First World War: the cult of hiking and country-walking.

In Britain, there was the Ramblers' Association getting underway. In Germany, there were the Wandervögel, the wander birds. These movements stood for liberty, for going where you wanted. Students of the Bauhaus were themselves members of the Wandervögel. Klee's equation of drawing and walking, the linking of the free hand with the free foot, would have had a resonance.

But the history of art and walking goes back further, to the heroic foot-sloggers of the Romantic age. Remember the lonely traveller of Franz Schubert's song-cycle, Winterreise. Remember Caspar David Friedrich's painting of a great solitary figure, The Wanderer Above the Sea of Fog, standing on a rocky peak, turned away and facing mystically into the void.

Or remember Samuel Taylor Coleridge and his sublime fell-walking expeditions in the Lake District. "The clouds came on – & yet I long to ascend Bowfell – I pass along Scafell Precipices, & came to one place where I thought I could ascend, & get upon the low ridge that runs between Scafell and Bowfell, and look down into the wild, savage, savage Head of Eskdale/ Good heavens! What a drop..." Physical and spiritual join in exertion.

Fifteen years before Coleridge went to the Lake District, the draughtsman Francis Towne had made his own trip. It was already established as art country, famous for its wild and dramatic character ("picturesque" was the word). Towne's walking-drawing tour took him round Windermere, Ambleside, Coniston, Rydall Hall, Grasmere, Vale of St John, Keswick, Buttermere, taking in mountains, valleys, lakes and waterfalls.

Ambleside pictures its view from a high point above the town, perhaps from the church tower. It shows an upright scene, with the edge of the town, a stretch of flat fields in the valley beneath, then the sudden heights with their climbing woods, and the crests rising beyond. It's sunrise. The hillside is gloriously revealed by a light that comes from over the peaks behind us.

A vision: but everything is made out in clear outlines and clear areas. This is how Towne sees nature. He's not interested in molding 3D forms, or again in conjuring up vague atmospheres. He defines things with ink contours. He fills their boundaries with flat hues and tones. His pictures tell you what the world consists of. Each type of entity – grass, trees, hill, mountain – is penned around, made into a shape, given an colour-label, which distinguishes it from other entities/shapes. It's a kind of map-making.

This is Towne's method when he's depicting the stable features of a landscape. But look at the "tide-mark" of light and shadow that falls halfway up the hillside. Or look at the glimpse where, high up left, cloud and sky meet. Their borders are equally abrupt, but their edges are not demarcated with ink outlines There's only a division of tone or hue. It registers that they are insubstantial and transient natural phenomena.

There are fixed woods, hills, trees, rocks, houses – and then there are clouds, and cast shadows, and (in others pictures) reflections seen in water. The tide-mark of the shadow will swiftly sink. The clouds will blow across. They are signs of the changing times of day, the edges of the present moment.

But there are other linear effects in Towne's work, marks that are drawn in ink, lines that could equate with walks. Sometimes it seems they literally do. Look closely at the small white dwelling on the hillside, almost at the centre of the picture. See the line going up from it, on a leftwards diagonal. It follows a wiggling way. It surely traces a walking ziz-zag path.

Even where Towne's lines probably don't actually take the routes of walks, they are walking lines. They are not free doodles, because walking isn't free, least of all the kind of walking needed to scale and scramble up this rough and vertiginous terrain. Trace Towne's contours as they climb the edges of these steeps. They take the difficult and uncertain paths that walkers (like Coleridge) would take, as they mounted the grassy crags or crossed their ridges.

There are no lines in nature, it's sometimes said. But of course there are many, and many of them are the lines of pathways. Towne knew something Klee didn't: how a walking line goes.

About the artist

Francis Towne (1739-1816) was one of the most brilliant and original of the English landscape watercolourists. A provincial drawing teacher by profession, he travelled around sublime and picturesque sights – the Roman ruins, Alpine peaks and torrents, Welsh hills, Lake District scenery – and rendered them in firmly outlined shapes, in areas of pure and contrasting colours. The world is analysed into its separate parts. Every element is contained and identified. The technique makes nature, even when it is vast or violent, feel serene and luminous. Towne exhibited in his day, but fell from view. He was rediscovered only in the early 20th century. Like other Romantics (such as Samuel Palmer), he was cast then as a precursor of English Modernists. Later eyes have found his art packed with pre-echoes of post-Impressionism, Japanese prints, even – in his piles of Alpine forms – of abstraction.