The placement of the NPC will affect where players gather, especially for those essential NPCs. Players often need to interact with NPCs for certain actions such as selling items. Players will most likely gather around these NPCs.
If we want to separate the high-level players and low-level players into different places, we can distribute the NPCs that serve different levels of players in different places. Similarly, if the virtual world encourages the interaction between different levels of players, we can design a place with an NPC that serves a large range of players. For example, there may be two NPCs that sell different levels of items with expensive prices in the virtual world. We can add an NPC seller that sells all levels of items with a cheaper price in the place we designed to gather the players.
