I was really expecting the city to be in China, not Central America. This stems from the fact that Skye was found their and all the people from that village were Chinese. I'm guessing one of two things happened. Either the city can move (which someone online said it can) or these people are all outcasts from the city. The third possibility is that there's more than one city. If there was more than one, it's likely they're near ancient human settlements, so there could be another near Egypt or Babylon. However, if there were one near practically every ancient settlement, that would mean that most of humanity is Inhuman. Since that doesn't seem to be the case (at least according to Whitehall and Coulson's tests), the first two possibilities are more likely.
SHIELD does seem to be in the lead in the race to the city. They're already located the city, while up until earlier this episode, Whitehall thought the Diviner was just a weapon. He didn't know about the city until Whitehall told him. In fact, he doesn't seem to be aware of the carvings at all. The only encounter Hydra seems to have had with them was Garrett and when the Obelisk was activated. However, Whitehall didn't seem to make the connection between the two. When Coulson had Skye researching the symbols, she recognized them immediately when she was the Diviner in action. Whitehall probably won't realize the link between it and the GH325 serum until Ward sees someone get killed by the Diviner and recognizes the symbols from Garrett. However, he might not realize that it was the serum that made Garrett carve them. Coulson knows it was the serum that made him, Garrett, and the others make the ruins.
