Altitude

A moment of idle curiosity led to downloading a phone app for altitudes. It uses two systems: GPS and ASTER (a digital elevation model) and now, as I write, note I am sitting at either 402 or 396 feet above sea level (for 69p I doubt both readings). And what would precision look like? In a forest would the measurements be to tree canopy? The bench I sit on? Or somewhere beneath the leaf litter at my feet?

How do we begin to measure altitude? Charles Hutton used ‘0’ for the summit of Schiehallion, working the rest out in negative numbers. It took the OS half a century to decide what point would define sea level; the zero from which everything else would follow as negative or positive number.

The research, walking and writing have slowly led to drawing. Among the material on show this weekend will be 4 drawings of ‘Britain’ (give or take).altitude 1

Each consists of a delineation of one height, not unlike Marsigli’s isobath. In the first, the line is drawn at 25metres below sea-level, eng-land – literally ‘thin-land’ in German – appears a little fatter; Dogger Island emerges off the coast of Lincolnshire, and to the south, thin slices of archipelago adorn the Norfolk coast. It suggests ancient times, a map from a few hundred years after the land bridge with Europe was broken.

I was surprised how emotive each subsequent map was, it tugs at our feelings of Britain as ‘home’, our fears of inundation. In the second map, 50metres above (current!) sea level, the wash is washed away, the Thames estuary slices deeper into the Home Counties.altitude 2aaltitude 3The final drawing in the series is at 500metres: Britain reduced to a speckle of islets like the aftermath of some apocalyptic event. Schiehallion is on a watery skirted peninsula of the south eastern edge of the largest isle, and facing a broad estuary formed by the Tay and Tummel rivers. From the summit looking due west the scene would resemble what we see now, but to head down the flanks, instead of the wee burn where a second base-line for Hutton’s map was created, would be sea inlet – a loch.

It is interesting to note that his northern base-line was flooded years ago, a man-made inundation to create Dunalastair Reservoir. Imagine then, walking along the ‘shores’ of Gleann Mór, to catch a boat perhaps, but where to? Perth is sunk as is Edinburgh, Newcastle and London.

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