How many kilometers long is the Great Wall of China, counting all sections and branches ever built, per China's official 2012 survey (1 km ≈ 0.6 mi)?

Answer

21,196 kilometers

That's more than half the circumference of the Earth. The wall isn't one wall but a sprawling network built by many dynasties over some 2,000 years — and despite the legend, it is not visible from the Moon.

Source: China State Administration of Cultural Heritage (2012 survey)