Why does Government PLaza require different populations to build?

[TidBuryFukles]

I want to build Government Plaza in my capital. It has a population of 4. It says I can't because I need 7. Yet in another city of mine which also has population 4, I can build it. Does anybody know why that is?

[iamjamiam]

Because it is a district. You have probably already built to the district population limit in your capital, but not yet done so in the other city.

[gimmethegepgun]

Cities can build 1 district, plus an additional 1 for every 3 population (meaning 2 at 4 pop, 3 at 7, etc). This doesn't apply to Neighborhoods or Aqueducts, and I don't think it applies to the space center.
Germany can build 1 more than this, and there's a great person that increases the number of districts a specific city can build.