Dusseldorf worth 4 with 18 million inhabitants
Madrid worth 8 with 3-6 million inhabitants
Vigo worth 2 with 4 million inhabitants
Merida worth 5 with 1 million inhabitants
I'm not sure where you're getting those numbers from, but they're just completely out of whack and honestly I think you just made them up on the spot.
Dusseldorf has nowhere near 18 Million people regardless of how you look at it. Dusseldorf the city has a population of 604,527, which is what I used to determine the bonus value.
The Urban area has 1,220,000 inhabitants, and the Rhine-Ruhr metropolitan region contains 11,300,000. However, neither of these are anywhere close to 18 Million, and neither are what I used to determine the value of the bonus.
Madrid's population is 3,141,992, almost 6 times that of Dusseldorf. While the Urban area has 6,183,000 inhabitants, and the metropolitan area 6,489,162, again neither of these are what I used to determine the bonus value.
The Merida one is a mistake; I accidentally used the population for Merida, mexico as a guide rather than Merida, Spain.
However, your numbers are again just completely out of whack. Merida, Spain, has a population of 58,985, and Vigo 294,997(481,268 Metro).
EDIT: More fake numbers to debunk:
Marseille worth 5 with 5 million inhabitants
Nantes worth 2 with 6.7 million inhabitants
Marseilles - 852,516, 1,560,921 Urban & 1,831,500 Metro
Nantes - 284,970, 600,502 Urban & 873,133 Metro
Edited 1/25/2016 20:32:21