HENRY the Navigator must be turning in his grave.

I probably do not need to remind the erudite readers of this organ that Henry was so-called because he was a great explorer in the days - the early decades of the 15th century - when Portugal was a mighty sea power.

During his reign, Portugese sailors reached parts of the globe hitherto unexplored and discovered, among other future holiday destinations, the Madeira Islands, the Azores and the Cape Verde Islands. To assist them, he employed scores of cartographers whose maps were to prove invaluable to future travellers. It is perhaps fair to say that he was mad about maps for, without them, he realised, it was terribly easy to get lost.

Of late, however, maps so loved by Henry and me - printed on cloth or paper - seem to be going the way of Onion Johnnies. To blame are satnavs and smart phones which are apparently responsible for the monstrous decline of sales in traditional maps and road atlases, which have fallen lately by over 40%. Meanwhile, Ordnance Survey, the country's principal mapmaker, has seen its revenues decline by £2 million to £8.1m over three years, leading it to conclude that its customers would rather use computers to get around than consult a map. Verily, it is the end - or very near it - of an era.

I have always loved maps, be they fantastical or factual. As a boy I took my lead from Robert Louis Stevenson who, famously, wrote Treasure Island after drawing it while on holiday at Braemar. Thus what began as a few doodles on a dreich day to amuse his stepson eventually became one of the world's best-loved books. In Stevenson's day, maps were of huge importance militarily.

Ordnance Survey, as its name suggests, was originally founded in 1746 by King George II to provide reliable information about the terrain of the Highlands in the aftermath of the Jacobite rebellion a year earlier. Where previously troops had ventured into terra incognita, now they would have at least a clue as to their whereabouts.

But Scotland was surveyed long before then. Our first cartographer was probably Timothy Pont, a graduate of St Andrews who, in the late 16th century, undertook to map in detail the whole country. Why he chose to do this remains something of a mystery. Like his father, who was a friend of John Knox and an adviser to James VI, he was a clergyman, and well-connected. There may be a perfectly innocent explanation; he may just have done it out of curiosity. Alternatively, he may have been acting on behalf of those who understood that knowledge is power and that to know the lay of the land gave them a valuable advantage over others with only a hazy appreciation of it.

Over the centuries, the science of cartography advanced in leaps and bounds. At its forefront was the Edinburgh firm of Bartholomew, which produced reliable and relatively inexpensive maps for a populace eager to explore parts of the country Pont could only describe as "extreme wildernes".

Growing up, I pored over them as avidly as I did any book, my fingers tracing the spidery course of a river to its source. The idea, imparted by enthusiastic geography teachers, was to recreate in the mind's eye the terrain drawn on a piece of paper. You could tell how steep a hill was by the closeness and colour of the contours. A climber who couldn't read a map was a danger to himself and others. To venture into the great outdoors without one was akin to taking a drive in a thunderstorm in a car without windscreen wipers.

Given my addiction, I ought to be a reliable map reader. That I am not was embarrassingly exposed not so long ago en route to Drumlanrig Castle. The chauffeuse did as instructed but, no matter how many left or right turns I asked her to take, we never seemed to get within sight of it.

Eventually, patience evaporated and the car scrunched to a halt and I was removed from my duties. It transpired that I had misread the index and that we had spent several hours looking not for Drumlanrig, Dumfries and Galloway, but Drumlamford, South Ayrshire. It could have been worse, I suppose. I could have been directing us toward Drumnadrochit.