Approval rating vs morale
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GalCiv2 Forums
What is the difference between morale and approval rating? When you hover above approval rating, it shows something about morale, I could assume that it is the same thing, but very often morale has different value.
The biggest alternate factor is taxes, but improvements, racial abilities, starbases, planet quality, overcrowding, and much more all influence what your exact approval rating is on any given planet. Your overall approval rating is a weighted average, each planet carrying a weight equal to its population. So keep your big planets happy and your overall rating will be good.