I doubt I'm the only person to notice this, but I'm almost mid way through my first game and it seems production is everything. In Civ 5 and Civ Rev I would hammer out population as fast as I could. You cant spam population growth and wonders any more but there is no reason not to have as much production as possible. You're always going to want districts and builders. If it's true it will inform how I play from now on.
Your # of districts is tied to your max pop I believe.