Which is the biggest missile test centre in the world?

Poker Flat Research Range (PFRR) is the world's largest, land-based rocket range. It has a chain of downrange flight monitoring, observing and recovery stations from inland Alaska to Spitzbergen in the Arctic Ocean.

Poker Flat is a sounding rocket launch facility 30 miles northeast of Fairbanks used for auroral and middle to upper atmospheric research. It's operated by the Geophysical Institute of the University of Alaska, Fairbanks.