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We get a lot of questions about course accuracy. Some of them are simple questions about certification, but most of them are about the discrepancy between your GPS device and the advertised distance of the race. No one wants to run a 5.2K, right?

The way road races avoid that 5.2K (not to mention the dreadful 26.5K marathon) is through a highly exacting (many would say tedious) process called course certification. This method has been around for decades and is considered incredibly reliable.

Certified courses are measured using a device called a Jones Counter – which you attach to a bicycle. The bicycle is then ridden in such a way as to ensure that it takes the “shortest possible route” on a given course. Over the course of multiple rides and multiple calibrations of the Jones Counter, corroborating data is recorded by the measurer.

The overall process is rigorous, exacting, and reliable. However, to be sure a course is never short, a fudge factor called “A Short Course Prevention Factor,” is incorporated, adding a few feet for every mile. So, a certified course is always a bit long.

The most important takeaway here is that if a course is certified, you can be assured it will be accurate. All NYCRUNS courses are USATF certified, and in addition to the colorful maps historically found on our race page, you can now find this more arcane source material.

So, why the heck does my GPS device say I ran 10.5K on Governors Island this morning? Well, there could be several reasons. The first one is that it is highly unlikely you will run the “shortest possible route.” If the course is an absolute straight line, it might be possible, but outside of some mile races most courses have a fair number of turns. The more turns a course has, the more distance you are likely to add.

There are also unavoidable choices the race director might make that could lengthen a course (never shorten!). For instance, if there is a last-minute construction project on one side of the street, you might avoid it and add a bit of distance in the process. However, we’re talking dozens of feet at most, not tenths of a mile.

As for your GPS device, it’s even less accurate than you are! But before we get into a war with the machines, let’s stop and pause to think about how amazing GPS is.

When GPS entered the running scene in 2003, it was a real game changer! The watches were super clunky, certainly not possessing the polished aesthetic of an Apple Watch. In addition to their less than stellar looks, the technology was not nearly as refined as it is today. And even though they’ve come a long way in the last 20 years, they are just not capable of being that precise.

There are other factors that can impact GPS as well: tall buildings, the weather, alien invasion, etc. However, if you use your GPS in a race, there is a way to get improved performance. Instead of relying on your device to note splits via auto-lap, you can turn auto-lap off and do this manually in line with each mile marker. This way you can feel confident that if you press the split button at the first mile marker, you ran one mile in whatever time your device says. Same thing when you reach mile 2 and so on.

Having said all that, you now know just about everything most athletes need to know about course certification and GPS. If you want to dive down the rabbit hole that is USATF Certification, you can learn more here. If not, you can feel confident that the next race you run with us will be accurately measured and USATF certified.