Among the stats which contribute to your overall Park Rating is a point "Park Balance Bonus". How exactly is that stat calculated and what can I do to improve it?
The "Park Balance Bonus" is the ratio of the number of rides to the number of scenery items in your park. This balance bonus is a factor in how many guests appear at your park.
The "Park Balance Bonus" appears to be calculated by a one to one ratio based on dollars spent in the appropriate category. To achieve the perfect ratio (1.00), For every dollar spent on rides, one dollar should be spent on scenery. This ratio is difficult to achieve as this is not typically the most effective strategy to create profit.
Source: ~/steam/steamapps/common/planet coaster/win64/ovldata/content0/main.ovl
Additional Reference: http://www.planetcoasterstrategy.com/planet-coaster-park-management-screen/