The 556 unique cities randomly selected are represented on the map by this sign:

The two hemispheres are separated by the equator, represented by this sign: ----

As we can see on the map, the distribution of land is very uneven between the two hemispheres:
nearly three quarters of them are north of the equator with almost 90% of the population.

That's why, in the visualizations we have more data from latitudes superior to 0.
And because there is almost no land between 50 and 65 degrees south, we have few data from this area unlike the North.