In honor of a very special Pi Day, Smithsonian Magazine posted this map that explores the human-made and natural structures that come closest to a perfect circle.

With apologies to 1990s alt-rock fans, a perfect circle cannot exist outside the realm of mathematics. From subatomic particles to carefully built structures, nothing in the physical world passes the perfect circle test, where every point on the circumference is exactly equidistant from the circle’s center. That said, some notable natural forms and human-made buildings get pretty close. Occurring either by happenstance or designed to pay homage to the shape that the Greek scholar Proclus called "the first, simplest and most perfect form,” these sites highlight the singular symmetry and symbolism the circle embodies.

Read more at Smithsonian Magazine