What is Nisab and why does the Nisab rate differ in each state?

What is Nisab and why does the Nisab rate differ in each state?

Nisab is the minimum threshold of wealth liable for zakat (that has completed a haul – one full year).
Nisab is calculated based on the current price of 85 grams of gold.
The rate of nisab differs among states because gold prices vary based on each state's reference source.
The State Islamic Religious Councils have the authority to determine the nisab rate, local customary practices (uruf), and zakat regulations based on fatwas and local economic conditions.