Data is missing for 4 more Line 4 stops the way your Beijingologist has it in his secret Subway Database, but from what we've seen in the stats, Line 4 seems to be yet another one of those boring lines where nearly all stops feature island platforms -- and when doors will always open on the left -- or nearly always.

There will be a few platforms of note, though. Haidian Huangzhuang (a Line 4 - Line 10 interchange) has Line 4 on a central island platform, but you'll probably need to figure out your direction of travel when flipping over to Line 10, which is Bagou- or Jinsong-bound, depending on your whim. This equally perplexing situation manifests itself at the Lines 5-10 interchange at Huixinxijie Nankou (God that's an awfully long name!).

Also of note is the planned cross-platform interchange at the National Library station. If you're heading south on Lines 4 and 9, or north on both lines, you benefit the most -- just walk across the platform and -- boom. Interchange finito. However, the Line 9 platforms are still pretty much -- well, they look like a prison cell from pics your Beijingologist has seen.

Incredibly easy is the Lines 2-4 transfer at Xuanwumen -- which is a bit like Chongwenmen (Lines 2-5) but features shorter passageways.

A rare case of malware has taken the Beijingology.com page hostage, and the linked Twitter account @Beijingology seems to be hanging by its last legs as it suspends itself into thin air. Oh well, there's still hope: follow David on Twitter to find out more about the Jing -- especially if it's got something to do with the Beijing Subway!