RRRC's FAQs page is under construction.
If you have heard any common questions about the club, our races, our competitions, or running in RVA, send the question (and ideally your suggested answer) to firstname.lastname@example.org.
Short answer: you need to learn to "run the tangents." The measured course is the shortest possible distance a runner can take. The longer the course, the more turns on the course and the greater the number of runners, the harder it is for a runner to run all of the tangents perfectly and follow that measured distance.
For a longer answer, we refer you to the Runner's World story "Is your GPS watch accurate on race day?"