Because, like, electricity travels at the speed of light, right? If you can make a phone call anywhere in the world instantly, how come your speed test results are so different if you test from different areas? That doesn’t make sense, does it?
First of all, let’s get this out in the open right now: electricity travels at the speed of light but the speed of light isn’t always the same. You know that number you learned in school… 186,000 miles per second? That’s the speed of light in a vacuum. When you’re talking about speed over a piece of fiber optic cable or copper wire the number is quite differently. Most web sites will punt at this point and tell you the number varies wildly but if you add up all the fuzzy math it looks like most sites get to about 15,000 miles per second which is a lot slower than that number you learned in school. So yeah, that’s a part of it.
The bigger part, though, is something you’re very familiar with if you live near a major city: congestion. Every time your data goes out in the world, it’s making a trip filled with intersections, virtual stoplights, slow onramps, all the stuff you urban dwellers know so well. Those branches on the internet may happen really, really quickly but add up enough of them and they’re going to slow things down.
Remember too that sometimes the major “pipes” that make up the internet can get overloaded, and the “interconnects” that connect the whole internet to your internet service provider aren’t infinite. Netflix subscribers nationwide are well aware that sometimes, things bog down.
So, if you’re into internet bragging rights, make sure you test the closest possible server. On the other hand, if you’re curious about how well you’re actually going to get to somewhere on the internet, test your speed to some of the major data centers in this country: Denver, central Kansas, San Antonio, etc. If you’re curious about where your favorite web site is physically located, you can use a tool like IPLocation to get an idea, then do a speed test to that general location. It will give you a much better idea of the real speed you’re going to get once you get done staring at those essentially false speed test results.