By default, Blender's particles don't have any spatial extension. This is fine as long as particles are rendered as halos. But if you give them a size and an appearance as object, it becomes obvious that they're able to go through each other.

What tricks can be pulled off to fix that problem?
For example, if you want to fill an area with houses, toss some leaves onto the floor, or just want charged balls to stick to each other.

I'm aware that a precise solution of this problem is very challenging -- but already some kind of approximation would do in most cases.


Question: What do you call a customer's customer in a specification document, use case, or scenario?
Answer: Maybe a bit of a tangent but...

I'm fond of interaction design myself, and there you never use abstract "roles" or "users" but something called "personas". Basically you make a up a character with a name, description and photograph and then you use that in your design process

"Bob is a bank manager in his middle years, he has some computer experience but is not especially fond of them."

Then in your project you can use their real names "No, Bob wouldn't want that" , "If Bob does this then Alice needs to be notified somehow". Personas are especially useful when you're doing scenarios.

I'd highly recommend The inmates are running the asylum and About face