THIS week there is a kind of upheaval on the Scottish orchestral scene. Everyone's on the move. The RSNO has just arrived back from a tour of Spain with its star soloist, violinist Nicola Benedetti. The BBC SSO, meanwhile, has just left Scotland for a tour of China - also with Benedetti, who has scarcely had time to unpack, repack and gather together the music for her punishing schedule of violin concertos.

The Scottish Chamber Orchestra is also lined up on the launch pad for its summer tour of Scotland. That begins tonight in Langholm, where the orchestra will be directed by the Swiss conductor Baldur Bronnimann. Now that, compared to glitzy, showcase international tours of Spain and China, might sound like small beer. But the SCO summer tour is a major enterprise, and one critical to any perception of the orchestra as a national company.

Between tonight and late July, with an extra slice of the musical cake added on at the beginning of September, the SCO will give a concentrated programme of 26 concerts - more or less the equivalent of a full winter season - that will pretty much saturate Scotland from top to bottom, north to south and east to west.

The tour will deploy no less than eight conductors or directors, including familiar figures such as Scotland's Garry Walker; the aforementioned Bronnimann, fast becoming an SCO regular; current and former leaders of the SCO Christopher George and Alexander Janiczek; and new and new-ish faces on the SCO podium including the Austrian conductor Aleksander Markovich, Simon Rattle protege Robin Ticciati, and Christoph Konig, currently in China with the SSO.

Where will the 26-concert tour go? Just about everywhere, from Langholm, Galashiels, Newton Stewart and Duns to Arran and Orkney; from Portree and Fort William to Aboyne and Cromarty; from Findhorn to Falkirk, and St Andrews to Paisley. What will the SCO play? Pretty much everything from the mainstream of western classical music, from Purcell through to Michael Tippett and Judith Weir, via Vivaldi, Bach, Haydn, Mozart, Beethoven, Mendelssohn, Weber, Tchaikovsky, Faure, Strauss, Elgar, Honegger, Stravinsky and sundry other composers.

The summer season is structured in a series of geographical blocks, with the south-of-Scotland tour opening tonight. The Highlands tour will have four separate strands, playing through early June and mid-July. There will be one residency (by invitation) at the St Magnus Festival in Orkney in late June, and another at the East Neuk Festival in Fife at the beginning of July. A Central Scotland tour, scrupulously avoiding the SCO's main winter-season territories of Glasgow and Edinburgh, will run in early September.

Such lists are a bit prosaic, and little more than a gloss on what is actually going on here. None the less, they are the nuts and bolts that constitute a remarkable Scottish enterprise that began 30 years ago, when the SCO was very young, and has, in recent years, undergone a dramatic expansion that gives the orchestra a unique geographical grip on the musical infrastructure of Scotland.

For decades, funding officials of the Scottish Arts Council, along with politicians of every hue, have agonised over and been irritated by the concept of heavily funded musical organisations that carry national status, but essentially operate a city circuit that has left vast population areas deprived of music from them. Though not operating to a political agenda, the SCO's annual summer tour of Scotland more or less precisely addresses the concerns of financial and political authorities. And one man, essentially, is behind the entire initiative: the orchestra's chief executive, Roy McEwan.

When McEwan took over the SCO management, 15 years ago, the Highlands Tour, now in its 30th year, was already well established, though it operated in a different, less mobile form than today. McEwan introduced the concept of dividing the orchestra into two groups, the strings and the winds, and sending each off on a different route at the same time, effectively doubling the territory reached, while coupling these ventures with full-scale orchestral concerts in similar geographical areas.

As that developed, however, he had his eye on another area ripe for cultivation: the Borders and the south of Scotland. Being a Dumfries man himself, he was well aware of the huge geographical and population area that was not being served by the national music companies.

Five years ago, having secured three-year lottery funding, McEwan launched the concert series. After that initial period, he "cobbled together" the funding to sustain it. Now it is on a more secure basis, targeting towns across a broad southern sweep where there is little or no provision of orchestral music.

"We're trying to build up an identity with certain venues, but never to have exactly the same circuit each year," McEwan explains. There is no master plan: "It has just evolved."

The most recent stage in the summer touring programme, the central-Scotland tour, launched last year, provoked some comments along predictable lines: the central belt is the SCO's bread- and-butter trail in the winter season, so why retrace its steps in the summer?

The tour developed out of internal discussions, says McEwan. "There was an assumption that people on the central belt, but outside Glasgow and Edinburgh, would travel to the cities. They didn't." So the SCO, surveying towns on the central belt and knowing from its own research that there were populations not travelling to the axis cities for concerts, extended the "remote areas" philosophy to take the SCO to the people. This year, the orchestra will visit Motherwell, Falkirk, Paisley and Dunfermline, and switch the central-Scotland month from May to September, when, reckons McEwan, there will be "a greater sense of momentum" as the SCO comes out of its big festival period and begins limbering up for the winter season.

The costs for the entire summer season are intriguing. The 37-strong SCO is a non-contract, freelance orchestra. Only when they play do they get paid - and the steady expansion in activities through the summer season has brought audible comments of relief from many players, who were increasingly concerned about the drop in income through the summer months. The budget for the 26-concert summer season, which I guessed at around £1m, will in fact be £230,000, with the bulk of it, in McEwan's words, "coming from the public purse".

That, in a well-packed, 26-concert season, is a lot of music for very little money. But apart from any intrinsic artistic value in the summer project, the fact that it is systematically getting high-quality live classical music to the least-served and most remote parts of Scotland is, one can only imagine, an investment beyond calculation in the broadest political sense.