This is an excerpt from Discovering Orienteering by Orienteering USA,Charles Ferguson & Robert Turbyfill.
Finding Attack Points
An attack point is the closest feature to the control that you know you can find and from which you can then find the harder-to-locate control. Using attack points is the most important technique that you will ever use in any form of land navigation. You must be able to clearly identify the attack point on the map and on the terrain. Because the attack point is something you know without any doubt that you personally can find, it may not be the same for everyone. It is the last thing you expect to locate before your final approach to your destination. Every leg of the course has an attack point. On a short leg, it may be that you will make your final approach from your current control, in which case the control you are leaving has become your attack point. On a longer leg, you may aim for an intermediate destination such as the edge of a pond. That location becomes your attack point for the control.
In an earlier example from the land navigation training at the Marine Corps TBS, the student guessed where the instructors would logically park their Hummer to walk into the woods to the control location. Noting that there were drivable roads and a close location from which the instructors would know exactly where to start for the control, she would run to that easy-to-find location, not knowing that such a location is called an attack point.
As noted, it is difficult to follow a straight line in precision compass reading for very far. Remember also that for any distance over 450 meters, precision compass reading is practically impossible unless you are crossing an open field and can steer to a visible object that far away. Therefore, it makes sense to locate an attack point, preferably within 200 meters of the control, and then move, using the fastest possible approach (usually the appropriate rough skills) to arrive at that attack point, where you switch to one of the two precision skills. Using distance estimation by measure and pace the whole way will also keep you from making errors.
What are some attributes of good attack points? First, they have to be easier to find than the control itself. Second, they should not take you too far out of the way. Third, they should be quicker to locate than the control. Fourth, they must be readily identifiable. And fifth, when you reach the attack point, you must know you are there.
Attack points are often much larger features than the control. In the TBS example, the student used either a crossroads or an intersection of one road into another.These are large and generally easy to see on the map and on the ground. The corner of a lake or a pond often shows well on the ground and the map, as does a readily identifiable field, making all three good attack points. Again, be alert if there are a number of ponds or fields close by so that you do not assume you are at one field or pond when you are at another. The dreaded parallel error (see the sidebar) probably torments orienteers more than the dreaded 180-degree error (see chapter 4). Keeping the map oriented to the terrain and perfecting the skill of distance estimation are key to avoiding a parallel error.
In going from the start triangle in figure 5.1 to the first control, an obvious, fast, and easy-to-find attack point is the path junction to the east of the control. In this map the dashed red line simply connects the controls; it does not show your route. My preferred route would be to run at an angle to the path on my right and then move as fast as I could to the path junction, which would be my attack point. Experienced orienteers might use the small hill upon whose edge the control is located as their attack point. Going from control 1 to control 2, the northeast corner of the westernmost pond is an excellent attack point. On the other hand, note the possibility of a parallel error if you are actually at the other pond to the north while thinking you are at the southern pond. Proper distance estimation helps to prevent any parallel error with the third pond, which is much too close to control 1. Navigating from control 2 to 3, you have a choice of attack points, either the edge of the field, the pronounced bend in the stream, or if you wish to get closer, the building beside the trail. None is particularly better than the others; they simply illustrate that you may have several choices for an attack point—just pick one and go.
What is the attack point from control 3 to control 4? If you used the skill of distance estimation and you learn that control 4 is only 135 meters from control 3, you can use control 3 as your attack point and follow a compass heading to control 4. Remember, control 3 is easy to find (you are already there!), and it is a short enough distance to use precision compass reading. If you thought you had to have another attack point such as the large boulder to the east of point 4, at least you have the process down cold. Just don't forget that your attack point should not take you too far away from the control you are trying to find, and in this case the small hilltop may be easier to locate than the large boulder.
To sum up, the technique of finding an attack point requires the orienteer to find a more easily locatable place (or point) from which to attack the control. It must be easier to find than the control, not too far out of the way, and readily identifiable on the map and on the ground. Remember also that the best attack point may be behind the control, forcing you to run a little farther but insuring that you find the control quickly. You should always select an attack point. Some orienteers eschew using an attack point for each control, but as with distance estimation and other skills, techniques, and processes, we can say, “That works for those orienteers—until it doesn't!” In other words, orienteer correctly and it will serve you well. Get sloppy and you may get away with it for a while, but bad practices will eventually betray you.
Learn more about Discovering Orienteering.