Which towns/areas within both Germany and the wider ZV have seen noticeable population decline due to emigration out of these areas towards the more cosmopolitan/modernist port cities?
Vienna, Elsass-Lothringen, Saxony, southern Franconia and Swabia, Rural Prussia and Rural Bavaria probably all see some degree of drain northward. In general, the German Empire's axis is continuing to shift north and eastward. For Vienna it is mainly a matter of going from the capital of an empire to the premier city of a major German state, a considerable bureaucratic downgrade which nevertheless keeps the city significantly larger than IOTL. As for Elsass-Lothringen the region is a bit of a peculiarity. There are a good deal of business opportunities in the area and cross-border trade with the French, but as a potential battleground it is subject to a lot of the Franco-German pressures and a considerable military presence. This has led to a steady stream of French-aligned citizens migrate across the border, while others look for educational and business opportunities in the empire's other cities.
Hamburg is probably the single quickest growing city of all in the Empire, contesting for largest in the empire, with Berlin and the Ruhr - stretching towards the Low Countries also seeing continued significant growth. Prussian cities grow considerably alongside the general coastal development. A region which sees major population shifts is Austria where Trieste grows into one of the premier cities of the empire due to its key role as an access point to the Mediterranean/Adriatic as well as its position on the trade from Italy. A great deal of oil also makes its way by ship from the Mediterranean before being offloaded in Trieste, particularly from the growing oil fields of Albania but also from the Ottoman Empire, with the Baku-Berlin rail-line being a bit too congested to contain all of the oil being shipped out from the Ottomans.
There has recently been a decided growth in sea and lake-side vacation destinations coming to the fore as more people find the time and resources to enjoy their free time, and while places like Saxony and Franconia are seeing a population decline, they are often favorite destinations for city-dwelling youth and adult movements of varying sort. The Empire is getting a great deal more urbanized and city-oriented, with rural populations generally declining as tens if not hundreds of thousands stream to the cities on a yearly basis.