This is the 14719th most frequent Russian word.
петербуржцы
Residents of St. Petersburg.
This sentence uses 'петербуржцы' as a general noun referring to all people residing in St. Petersburg in a broad sense.
Петербуржцы любят проводить время на набережных Невы.
Residents of St. Petersburg enjoy spending time on the banks of the Neva River.
Here, 'петербуржец' is used as a noun inflected in the dative case to refer to someone personally identifying as a resident of St. Petersburg.
Как петербуржцу мне приятно ходить в Эрмитаж.
As a resident of St. Petersburg, I enjoy visiting the Hermitage.
In this example, 'петербуржцы' refers to the collective cultural identity of St. Petersburg's residents.