From the slopes of Schiehallion to the dunes of Barry Buddon, something is stirring this week in the more remote parts of Scotland. Nearly 4000 orienteers, aged from five to over 90, are locked in a sport where Scotland has developed a global reputation.

Competitors from more than 30 countries have flocked to Tay 2009 for the Scottish 6-Days Orienteering event. Some are using it as a warm-up for the World Championships, which start in Hungary on August 16.

Some but not all. Scott Fraser, who is Scottish Orienteering's professional officer, and three-times British sprint champion, is in the team for Hungary, but he is deputy co-ordinator of this week's six-day event. He and fellow GB team-mate Graham Gristwood tested the course for the opening race designated by the International Orienteering Federation as a world- ranking event. For either to take part would be akin to insider trading.

There are six events over seven days, and tomorrow's will be the 100th in the series which dates back to 1977, but the sport's debt to Scotland goes back a bit further than that. To 1774, when the astronomer royal, Nevil Maskelyne, allegedly bankrupted the Royal Society with an experiment which led to the invention of contour lines. For which competitors were doubtless suitably grateful as they navigated their way round the mountain yesterday.

Six individual competitions are on the calendar, with today being a rest day. Mountain-bike orienteering and sprint orienteering has been arranged for those suffering from withdrawal symptoms.

The hub is Perth Racecourse, at Scone. Over the past three days there have been events at Dalrulzion (near Blairgowrie), Kinnoull and Tullochroisk. Tomorrow they are Tentsmuir, followed by Barry Buddon, where the army shooting ranges will be closed, and finishing on Saturday near Dunkeld at Loch Ordie.

Although some of the world's top competitors are in action, there are courses for beginners, including children as young as five who follow stringed courses for which entry is possible on the day.

It is very much a family affair. The co-ordinator, Gareth Bryan Jones, ran for Scotland in the steeplechase at the 1970 Commonwealth Games in Edinburgh. He won the Scottish over-60 orienteering title earlier this year. He says that like Fraser, he'd love to be competing, but with organising the event (effectively a full-time job for the retired biochemist) and knowing the courses, that is not possible.

But he highlights how much of a family sport this is. His daughter, Kirsty, is a former GB internationalist and World Universiade medallist. Now 39, she was competing yesterday. So was husband, Simon, and their children Ellen, seven, and Euan, five.

It's also an event in which the elite from other endurance sports often excel. Competing this week is 39-year-old Cartsen Jorgensen. The Dane, known as "The Moose" for his ungainly action in the days when he was European cross-country champion, was lying fifth in the elite class after the opening two races. He concentrates more on orienteering, because he says it's "more fun".

Scott Fraser twice represented Scotland in the World Mountain Running Championship and played a trial for Celtic. He will be in the British team in Hungary which defends the world relay gold.

The event lost its oldest competitor, 90-year-old Englishwoman Elizabeth Brown, when she withdrew after sustaining an injury at the start line, but several others are over 85.

As people grow older, peak fitness declines, but better map-reading skills often mean that older competitors can triumph.

The six-day event is a legacy of the first staging of the world championships in Scotland. They used the maps to host the first six-day event the following year and have held it every two years since.It is backed this year by Perth and Kinross Council; there's funding from Eventscotland and it's reckoned to be worth close to £1m to the hosting communities.

Social events feature strongly, just as they did on Schiehallion after the contour inovation more than 200 years ago. In the ceilidh they held then, the premises were burned down. A certain amount of angst has been expressed on the unofficial Scottish athletics website, and to this newspaper, about the fact that the Ethiopian team at the Falkirk Cup three weeks tonight are to be ineligible for prize money.

Other teams and invited guests will be eligible for maximum winner's prize money of £500 for any individual event.

Critics suggest this is discriminatory and a potential "public relations disaster" for the sport. After all, they say all teams have been eligible for prize money at GB matches in Scotland, at Scotstoun and the Kelvin Hall.

Scottishathletics are, to say the least, indignant. Chief executive Geoff Wightman said last night that it is a private arrangement with the Ethiopian federation, who were "perfectly happy with the financial arrangements. They understand how the budget is worked out. It's costing three times as much to bring the Ethiopians here than it cost to bring the American juniors last year."

The Americans, mainly collegiate athletes, were as a consequence ineligible for prize money (under NCAA rules). And the sport can point to the fact that in the US, road race prize money is confined to US citizens. This not only prevents Kenyans from cleaning up, but also excludes Scotland's Andrew Lemoncello (who has a US as well as a British passport) from winning money in America.

But we understand there are moves afoot in some Scottish road races to exclude other than British nationals.