in a single moment, the data is collected at 00 hours 00 minutes of a certain day, which is approved by the Government. All births and deaths after this point are not counted in the current census. Then the data on all issues is aggregated into a single array, without personal data and given to statisticians, who show us the final figures for demographic, social, national and other aspects.
Oh, I wanted to write an answer, explaining that it happened in Riga, and the author turns out to be from Riga too!
So, we had it. A man came to our home, 25-28 years old, not very beautiful in appearance, with a computer bag, wanted to know everything about our family. But I was alone at home (I was 14 years old). He asked when his parents were at home and left. I came twice more - my parents were not at home. So he came again and finally found everyone. The questions were related to nationality, language (actually here), type of employment (you work for yourself, study ...) and something else on the little things. Parents were reluctant to answer, but the guy didn't press too much.