The sequence of the door numbers starts from the beginning of the street and the beginning of the street is its closest point to the city center and this is valid for all the streets.
What makes things complicated is that in the old part of the city the doors’ numbers follow the normal sequence 1, 2, 3, etcetera going starting from the right all the way to the end of the street continuing with the numbers on the left side of the street. So, if you are on a street that has one hundred doors, you have number one on your right and number one hundred on the left. But this is valid only when you are in the oldest part of the city, okay?
The numbers of the doors on most of the streets are assigned following an odd/even logic.
If you are at the beginning of a street, at door number one, you see that the next one is door number three and you find number two on the opposite side of the street. Than we also have A’s, B’s, C’s next to the door number, why? Because sometimes they built something new between two older buildings and so, instead of re-numbering all the doors on the street, they continued with the same numeration picking up from the last number before the new building.
If the last building was number 9 and the new building had three doors, they were numbered 9a, 9b, 9c.