The weight of any spell in the game is 12.5 and does not depend on the type of city. The exceptions are the following spells: Bless, Dimension Door, Town Gate, whose weight is 25.
Therefore, the probability of Bless appearing is 64%, and any other spell of the first level is 39%;
The probability of any spell of the second and third levels appearing is 25%;
The probability of Dimension Door and Town Gate appearing is 48%, and any other spell of the fourth level is 26%.