In a post called "What are These Giant Concrete Arrows Across the American Landscape?" we showed you a long-forgotten wayfinding device for early airmail pilots. The entry featured the map below, plotting out the course of the arrows that the pilots could follow to get cross-country:

The map atop this entry reminded us of that. Any guesses as to what it is? It clearly seems to indicate a cross-country and coastal travel pattern, except for the isolated island chain of dots centered in Texas. And you've undoubtedly noticed each red dot appears to have some sort of visual perimeter around it.

Still no guesses? Here's another hint: The map up top is what exists right now, but later this year it will look like this:

And by the end of 2014, it'll grow into this:

Finally, by the end of 2015, whatever these red dots are will have achieved U.S. dominance, except for a little sliver of Montana:

Okay, maybe it's unreasonable for us to expect you to be able to guess what these represent:These dots are locations for Tesla Superchargers, the electricity refueling stations that Tesla Motors is providing free-of-charge for Model S owners who sprung for the larger 85 kWh battery.

These Supercharger stations can reporteldy juice you up "16 times faster than most public charging stations," meaning 20 minutes will get you a half-tank, 40 minutes gets you to 80% and 75 minutes will get you topped off. If you're wondering why those numbers seem wonkily non-linear, it's to do with the peculiar math of electrical charging. As Tesla explains:

The fastest way to replenish your Model S is to charge to 80% state of charge, which is enough for travel between many Supercharger stations. Charging the final 20% takes approximately the same amount of time as the first 80% due to a necessary decrease in charging current to help top-off cells. It's somewhat like turning down a faucet in order to fill a glass of water to the top without spilling.

Some of the stations will reportedly feature solar canopies, though there's no way these are providing all the juice; they're simply meant "to offset energy use and provide shade."

The ramp-up in Superchargers seems pretty impressive, at least in the U.S. Europe's got it a bit rougher, as right now a Tesla owner in Germany can't get to Sweden or Norway by Supercharger stops alone:

They'll be able to later this year, however. Also, whatever lazy graphic designer drew these perimeter circles and didn't bother to map them to the outline of actual land should be castigated. What am I, driving fifty miles out into the North Sea?

By winter of 2014/2015, European Tesla'rs will be able to hit most of western Europe and will also be able to drive far into the Norwegian Sea, presumably to catch salmon from inside the comfort of their Model S.

Supercharger rollout in Asia is currently limited to the Chinese market, and only in two cities. If you don't live in Beijing or Shanghai, you ain't getting Supercharged.

In the near future it will get a little better, as a Beijing-based Tesla'r will be able to drive all the way to North Korea. But you'd have to be a real jerk to show your Model S off over there.

You can find specific addresses of current Supercharger stations here.