Martin Luther and the German Reformation's impact on cities is difficult to generalise about as each city reacted differently to circumstances unique to it; some converted near enough immediately while others took many years to decide. Others, even in north Germany, never converted to Luther.
In the early C16, there were 65 imperial cities (free cities) which were not controlled by a prince. In theory they had a direct allegiance to the emperor. 51 of these cities turned to Protestantism at one time or another. These conversions were not forced on the population as there seemed to be a genuine dislike of the Catholic Church. In Ulm, 87% of all votes cast in a straight forward vote between the Protestant and Catholic churches were in favour of Luther. Cities tended to be very pious possibly because the populations were better educated than rural areas and invariably contained lawyers, merchants etc. who would not be found outside of cities. It would be these type of people who would be well aware of the wrong doings of priests. Even before the input of Luther, Ulm banned a blasphemer for fear that God would punish the whole city as a result of one manís actions.
Cities had a much higher literacy rate than rural areas and printing presses would be found in cities and very rarely in rural areas. "Sermon addiction" was common. Some cities and towns endowed preacherships. In Wurttenburg, 31% of the towns did just this to satisfy public demand. Some preachers had much fame such as Johannes von Staupitz who was Lutherís monastic superior and Geiler von Kaiserberg.
The cities had also acquired a political conscience to protect themselves from prying princes. They had developed a bureaucracy to run themselves. These civil servants were educated humanists. It was people such as these who became ideologically more aware. University students, humanist entrepreneurs and groups such as these were very receptive of Lutherís ideas. The desire to maintain law and order meant that city fathers could not ban Lutheran preachers for fear of public disorder problems if a ban was imposed. City fathers had no love for the Catholic Church but they were fearful of the emperor and the more powerful Catholic princes. Many city councils were more forward and simply banned Catholicism - such as Nuremberg in 1525.
The process involved in banning Catholicism was simple : a Catholic delegate would face a Lutheran delegate in a "disputation" (academic argument) and the city magistrates would decide who had won.
Not all cities followed the example of Nuremberg with regards to the speed of her conversion. In 1522, Regensberg had shown support for Luther but it did not convert until 1542 for fear of angering the Catholic Duke of Bavaria.
There were many advantages in taking over Catholic affairs within a city. The most obvious involved money. A Protestant city simply took over Catholic property etc. Some cities used this newly gained money for charitable purposes (Leisnig) and Lutheran preachers used the Scriptures to defend these actions. In Strasbourg, Martin Bucer used lay elders to look after the cityís social welfare and to help discipline the general population.
However, finding accurate and specific information for all Germanyís cities has proved all but impossible due to a lack of evidence. 2000 cities have not been properly researched and so it is impossible to make any general comments about patterns found in free cities. The northern cities tended to convert to Luther. But Cologne in the north remained Catholic.