PC Town Npc Location & Mob Spawn Rate

[solarmadness]

Hi I got a question about town Npc's and does it matter where you place house's for town Npc's . So in my time of playing Terraria I've always made a house's for my Npc's on the surface of my world and mob's always spawn but recently I started making an underground base for my Npc's and I've been seeing less or no mobs spawning at all. I know that having some Npc's makes mobs spawn less the more they are in the location u put them in but in my other worlds and in the past mobs always spawn maybe like 5 mobs at a time maybe more if I'm boosting the spawn rate with a battle potion and a candle but when I use this items in my underground base no mobs spawn and some events that make mobs spawn just stops working unless I leave the area of my Npc's like around 200 blocks away from my base if someone can tell me why I'm not seeing mobs that would be awesome

 

[Cubic.]

It doesn't matter where you place an NPC home as long as there's no corrupted or crimtane blocks nearby.

As for mobs not spawning where you place your NPCs, I'm pretty sure spawn rates are lower underground.

 

[Sigma90]

The Wiki has a page on spawning - please see that page for specific details.
The key paragraph is: "The presence of friendly NPCs greatly reduces the rate at which enemies spawn, and also reduces the maximum enemies as well. When 3 or more NPCs, or the Skeleton Merchant are present, no enemies will spawn. Events such as Slime Rain, Pirate Invasion, Lunar Event, etc bypass this reduction."

Depending on how you built your surface houses vs. your underground base, the NPCs on the surface may not have been close enough to each other to reduce or stop enemies spawning. I get the feeling your surface houses were spread out and the underground base had them all together in one location? If yes, that's why you're seeing a difference in spawning.

The other thing to note is that NPCs stop enemies spawning, but still allow critters (birds, bunnies, etc.) to spawn as normal. The critters count towards the spawn limit too.

I hope that helps!