At the moment, evaluator only considers the number of adjacent completed cities when taking a field. But there is more to it than that:
Consider the number of the open sides of the field. Even when a field is seemingly big with many tiles, if it is already enclosed by roads or cities, then it may not be as valuable as it seems.
Consider the number of adjacent "incomplete" cities (and their complete probabilities)
At the moment, evaluator only considers the number of adjacent completed cities when taking a field. But there is more to it than that: