How to model whether or not a city is thriving? I'm working on a concept for a game that requires some statistical inference and I'm not sure how to go about it. My issue is I'm trying to come up with a way to calculate if a city (in the game) could evolve into a thriving city. 
I have a bunch of rules that rate different factors of the city like health quality, distance to the coast, population growth etc and I need to boil all to these independent scales into a single probability. At the moment I'm averaging all of the numbers, but I'm sure there's a better way about it. I also need to calculate a degree of confidence.
I've tried searching for a solution in books but they all cover simplistic scenarios with only one variable. 
I hope someone could point me to the right direction.
Thanks!
EDIT 1:
Since this is a game, I'm just using a few variables to decide if a city is thriving. Also since it's a realtime problem I cannot use stat methods that are based on training sets. 
I do not have a math background, so this is what I've understood from my research, so please feel free to correct me if any of my assumptions are incorrect.
 A: It sounds like you don't have a dataset which matches your explanatory variables (close to coast, etc) to your dependant variable (whether or not the city will thrive).
This means you do not have a supervised learning problem.
A simple solution to your problem is to have cities evolve by some basic rules.
For example:
Lets say that you have the 3 variables health quality, distance to the coast and population.
The rules could be:


*

*Distance to the coast increases health quality.

*Health quality increases population growth.

*Having a high population decreases health quality.


With specific numbers, these rules provide a transition function.
Then pick some initial values and iterate using a transition function. After a few thousand iterations, the values of population, money, trade, etc would let you determine whether or not a city is thriving.
This is basically setting up a bunch of differential equations and trying to find a steady state. Its kind of a complicated predator prey situation.
