Guide: How to calculate park rating?

[Deurklink]

Park rating is one of the least explained features of Rollercoaster Tycoon, but quite an important one as you need it to complete some scenarios. In this guide I will explain what park rating does and how it is calculated. This guide is based on OpenRCT2 (version 0.1.2). The code can be found at: 
https://github.com/OpenRCT2/OpenRCT2/blob/develop/src/openrct2/world/Park.cpp in the function calculate_park_rating().

What is park rating?
Park rating is represented by the green bar in the bottom left of your screen. Clicking it brings up a graph which shows a history of your park rating. The park rating is always a number from 0 to 999.

What does park rating do?
Park rating does two things:

1. In many scenario goals, the park rating needs to be above a certain value next to the main goal of having a certain amount of guests in your park, for example.

2. It helps attract guests. The higher your park rating, the higher the probability of a new guest spawning. If your park rating goes down a lot, no more new guests will enter, and the number of guests in your park will drop.

Which factors influence park rating?
Park rating is influenced by the following things (number in brackets is amount of points gained or deducted):
1. Difficulty of the park - A park can be set to have a higher park rating difficulty. [+1150 or +1050]
2. Number of guests in the park. [-150 .. + 3]
3. Number of happy peeps. [-500 .. 0]
4. Number of peeps who are lost, and cannot find the park exit. [-infinity .. 0]
5. Ride uptime [-200 .. 0]
6. Average ride excitement and intensity. [-100 .. 0]
7. Total ride excitement and intensity. [-200 .. 0]
8. Litter. [-600 .. 0]
9. Deadly casualties. [-1000.. 0]

How to calculate park rating?
Here I will try to explain step by step how the park rating is calculated. It has some calculations and some code examples.

Initial rating
The rating calculation starts with a value of 1150. In parks with difficult park rating, the initial value is 1050.

Number of guests in the park
The number of guests in the park is counted, and divided by 13. If there are more than 2000 guests in the park, the function just uses the value 2000. This division will give a result from 0 to 153. This number is subtracted from 150, which gives a result from -150 to +3. 
In short, if you have 0 guests, 150 will be subtracted from the park rating. If you have over 2000 guests, 3 will be added to the park rating.

Number of happy peeps
After this, the game counts the number of peeps who have over 50% happiness, and the number of peeps who are lost AND cannot find the park exit.

Every peep that has over 50% happiness is counted as a happy peep. First, the function will subtract 500 from the park rating. Then, the number of happy peeps is multiplied by 300, and then divided by the number of peeps in the park. If this value is higher than 250, the value 250 will instead be used. This value is multiplied by 2, and then added to the park rating.
In short, if you have no happy peeps in your park, you will lose 500 points of park rating. If more than 83% of your peeps is happy, you will lose no points of park rating.

Number of lost peeps
As shown in the previous paragraph, the game counts the number of peeps who are lost AND leaving the park. Up to 25 guests can be lost and leaving the park without it affecting the park rating. For every guest above these 25 however, the function deducts 7 points from the park rating. There is no limit to this deduction, so this can take the park rating all the way to 0! This is probably done so players don't block their park exit with a banner. When your park rating suddenly drops to 0, most likely many guests are stuck somewhere.

Ride uptime
The average uptime is calculated for all rides. Uptime is calculated as 100 - Downtime (Can be seen in the maintenance tab of a ride).

If the average uptime is 0 (all rides broken down), the park rating will lose 200 points. If the average uptime is 100, park rating will lose no points. When rides are broken down, you should always try to have them fixed quickly.

Average ride excitement and intensity
The game takes the average excitement and intensity of every ride (multiplied by 100, so excitement of 3.00 would be 300), and divides them by 8. The resulting excitement value should be as close to the number 46 as possible. This corresponds to an excitement value of 3.68. Resulting average intensity should be close to the number 65, which corresponds to an intensity of 5.20. The further away the excitement and intensity are away from these numbers, the higher the penalty.

Basically, to get no penalty from average ride excitement and intensity, you should probably have a good mix of gentle rides and roller coasters. The effect of this calculation on the park rating is quite small however, as it is maximized to 100 points.

Total ride excitement and intensity
The game takes the excitement and intensity of every ride (multiplied by 100, so excitement of 3.00 would be 300), and divides them by 8. Then all intensities are added to one another and all excitement ratings are added to one another. These numbers must both be bigger than 1000 to get no penalty. 
In short, if the total excitement of your rides is more than 80.00, and total intensity is also more than 80.00, you get no penalty. If they are both 0.00, your park rating will lose 200 points.

Litter
The game counts all pieces of litter in the park, while ignoring litter that has very recently been dropped. For every piece of litter, the game subtracts 4 points from the park rating, with a maximum of 600 points. When your park becomes very big, litter will play a bigger role in the park rating as having more guests usually means more litter will be dropped.

Deadly casualties
Whenever a peep drowns in the park 25 points are subtracted from the park rating, with a maximum of 1000. For every vehicle that crashes with peeps in it, 200 are added to the casualty penalty, as long as it is below 500. This penalty slowly diminishes over time. In parks that use no money, the penalty dimishes a lot faster for some reason.

Clamping
Finally, if the result of above calculations is a value below 0, the park value will be set to 0. If it is bigger than 999, it will be set to 999. 

Cheating
If you have trouble maintaining your park rating, or if you don't want to be bothered by it, you can force the park rating to a certain value by using the cheat menu. This cheat is found on the park cheats tab of the cheat menu.

Conclusion
It is essential to keep park rating high to attract more guests to your parks. This guide should help you pinpoint problems in your park. If you ever have trouble finding out what causes a park rating drop, feel free to ask for help. I have modified a version of the game so it tells me exactly how much each of the above mentioned factors affect the park rating 

Edited December 28, 2018 by Deurklink

[VincentsAnimations]

Holy crap! This is pretty meta. I always looked at the game as a philsophical challenge more than the math challenge. XD

[Deurklink]

I made a video for this guide which can be seen here:

 

[Krutonium]

I have a theory about the faster diminishing of the crash penalty on No-Money Parks. Specifically, I think the reason that was done was because if your park rating stays too low on a no-money park for too long, the park closes and you lose the scenario. This was probably done to balance that out - so that a deadly crash doesn't necessarily spell disaster for your park - Just a period of time where you have to be careful to manage your rating so it doesn't cost you the scenario. In a park where you have money, that isn't a factor, so having the penalty last long results in a financial penalty - Less or No new customers means you're going to have a financial slump. The result of course being that in either type of scenario, a crash is serious, but not enough to necessarily shut down your park, unless it was being mis-managed to start with.

Edited December 29, 2018 by Krutonium

[Deurklink]

On 29/12/2018 at 03:37, Krutonium said:

I have a theory about the faster diminishing of the crash penalty on No-Money Parks. Specifically, I think the reason that was done was because if your park rating stays too low on a no-money park for too long, the park closes and you lose the scenario. This was probably done to balance that out - so that a deadly crash doesn't necessarily spell disaster for your park - Just a period of time where you have to be careful to manage your rating so it doesn't cost you the scenario. In a park where you have money, that isn't a factor, so having the penalty last long results in a financial penalty - Less or No new customers means you're going to have a financial slump. The result of course being that in either type of scenario, a crash is serious, but not enough to necessarily shut down your park, unless it was being mis-managed to start with.

That could very well be the reason!