Not all the city names appear on the x axis of the previous plot.
We can change this by defining the xticks explicitly with "range(len((city_frame.index))".
Furthermore, we have to set use_index to True, so that we get city names and not numbers from 0 to len((city_frame.index):
city_frame.plot(xticks=range(len(city_frame.index)),
use_index=True)
New problem:
The city names are overlapping!