When was the last time a national or city census was held?
Depends where a person lives, doesn't it? They are done every few years in some countries and then, the countries like Finland that have very accurate healthcare data know exactly how many people are in the country.
Someone in Europe can't know the exact number of people in Johannesburg, South Africa
People in Jo-berg can't know either, since the records in some areas like the ghettos aren't well kept.
That's very true.