How Long Is the Great Wall of China?

I stumbled across an article this afternoon on msnbc.com claiming,

Great Wall of China more than twice as long as previous estimates

The first think I thought was, “Has nobody ever measured it before?” Sure, it’s long, but we know how far it is to the sun! Out of curiosity, I read the article. It was three sentences long and referred to a BBC article. Apparently, it’s actually 13,171 miles long instead of the length announced in 2009 of 5,531 miles, according to the Chinese government. Right here, there are two things that make me skeptical:

• The msnbc.com article only converted one distance from metric, and not the other distance–I did that for you. This makes me think the author was lazy and just looking for an excuse to post pictures of the Great Wall, which are impressive.
• The Chinese government announced something that makes China seem cool. Always a cause of skepticism in my book.

I read the BBC article, which was mainly about the Beijing officials’ decision to open more of the Great Wall to tourists, since the currently available portion is very crowded certain times. This leads to tourist scaling the wall in  unauthorized locations, damaging the wall. Maybe they’re just trying to get to the other side?

I did a bit of research into how and when the length of the wall was determined. The original Chinese media article was very helpful in this research.

• June 5, 2012, the Chinese-run news agency announced the wall was 13, 171 miles long, based on state survey results. “Previous estimates of the wall’s length were mainly based on historical records.” (Source)
• 8.2% of the wall built during the Ming dynasty is still intact. Much of the wall is way older and was more earthen barriers than the stone structure we’re familiar with. (Source)
• In 2009, a government mapping study announced the length at 5,500 miles, an increase from the previous estimate of 3,100 miles. The study was ongoing, so it’s not surprising there has been a new announcement.  A BBC article describing the study says the government used GPS and infrared technology to discover sections of the wall concealed by sandstorms.