I just realized that although I know how ski-o works, a lot of people have no clue. So, I thought I would try to explain.
The basic premise is that the racer is given a map with the locations of "controls" marked on the map. The competitor must visit these controls in the order indicated on the map, and the person who does so in the shortest amount of time wins the race.
The controls are white and orange flags, usually hung in a spot visible to the competitors. The controls are marked as a pink or purple circle on the map, with a dot where the flag is actually hung. In ski-o, the trails are marked in green. The solid green line indicates a wide trail, and the dashed green line indicates scooter tracks. Scooter tracks are trails just wide enough for a snomobile, about 1.5m wide. At the coaches' meeting the night before a race, the race organizer will announce how long the course is, via straight line distance, the amount of climb, and the percent of tracks that are wide versus narrow. The actual distance will be much longer than the straight line distance, because unlike regular orienteering, it is not fastest to cut through the woods in ski-o.
The competitors all have e-punches. These are little electronic sticks that have an elastic band that go around your finger, and when you get to the control, you stick it in a hole in a box and it beeps. That means that the punch has been registered and you can go on to the next control. If electronic punching is not being used, the competitors have a punch card, which is a piece of paper with a box for each control, and at each control there hangs a hole puncher thing with a pattern of pins that you punch in the correct box on your piece of paper.
There are a couple different formats for ski-o, just like in cross country. The sprint is about 2-3k (these distances are all straight-line distances), with 15-25 controls. The long distance is usually mass start, and should take the winners about 70-80 minutes, often 12-20k. The middle distance is shorter than the long but longer than the sprint, and is usually individual start. The relay is a mass start, and is like a cross country relay race but with maps and stuff.
Lets take the sprint as an example. The following map is at a scale of 1:5000, which is very, very detailed, and it is easy to get lost in the details. The other maps are at a 1:10000 scale. This race is individual start, so before I head to the start, I check that I have my e-punch, which I safety pinned to my glove, my race number is on, and I am wearing my map holder. Entering the starting pen, I must first pass an official, who has two e-punch boxes. The first is the clear box, the second is the check box. I stick my e-punch in the clear box, wait for the beep, then punch the check box and wait for the beep. Once I've been cleared and checked, I go line up at the two-minutes-to-go line. I wait there for a minute, then move up to the one-minute-to-go line. With 15 seconds to go, they give me my map. I have to quickly snap my map into my mapholder, and frantically find number one, figure out where it is in relation to the start, and figure out which way I'm going to ski. I usually get this done just in time before the clock does its last beep and I'm off.
This was the women's sprint course.
After I've found all the controls, in the right order, and I've crossed the finish line, I must punch the finish box, which an official is holding. Then I go to the timing shed, and download my splits. For the individual races, they "quarantine" the racers until everyone has started, so that there can be no sharing of information between competitors. So as I leave the finish, they take away my map (for the big competitions--the local ones, you keep your map. At the end of the week, they give all our maps back, but they don't want you to study the area or the routes too much in between races. Not sure exactly why, since everyone would have the maps, but that is how it is). Then I walk to the quarantine room, where I wait until everyone has started, at which point we can leave and go do a cooldown. Usually it is a 5-10 minute wait, but with more people it is a longer wait.
Speaking of warming up and cooling down--the competitors must stay in the area marked as warmup/ski testing. You are absolutely not allowed out onto the course, at least in the big competitions. This means a lot of time skiing in circles, or running on the road as a warmup.
For the long distance or relay race, both of which are mass start, the course "forks", meaning there are butterflies of loops around a couple controls, so that they can give different varieties of the course to each competitor, so there is no following, but everyone still ends up doing the same course.
I think I've about covered it... feel free to ask questions or ask for more information on something. I'll get the rest of the maps up soon.