https://forum.paradoxplaza.com/forum/threads/developer-diary-1-population-and-living-world.1857075/

Welcome to the first development diary for Europa Universalis V! That's right, Developer Diary! On the not so super secret game Europa Universalis V.
This time hosted by the community team, represented by myself PDX Ryagi. We'll be going over some broad topics, for deeper details and design philosophy we'd highly encourage you take a peak back at our Tinto Talks series. A handy megathread can be found here. But without further ado lets get talking about quite possibly the heart of EU5, Pops:

EU5 is the fifth edition of a franchise that spans over three decades of development, but this time, we’re introducing what can be considered a revolutionary approach to world simulation and population management, moving beyond the abstract numbers of its predecessors to try and create a truly "living world.”

Spanning the centuries from 1337 to 1837, we hope to immerse players in a historically rich and dynamic world where every decision has tangible consequences for both its inhabitants and the environment itself. The heart of EU5's living world is its "pops" system, which aims to simulate every single living individual that existed in 1337 at a granular level. Unlike previous version of the game, where population was a more generalized statistic, EU5 portrays individual working people, each with their own needs, wants, and roles within a nation.

Population Map mode of Hungary at the start of the game (1337)

These pops are the lifeblood of a nation; without them, buildings shut down, manpower is nonexistent, and colonies fail to populate. Managing your population effectively is a top priority, as they require feeding, work fields and industries, armies and navies to defend and expand, and even ready wealth for taxation and investment.

Burghers in Pest 1337