"in" versus "at"

Sure.
Imagine a couple of cosmic commentators doing a live cosmocast;

"There's nothing unusual to report here at the cruel world of violence. What's the situation over there at Bill's world of maple magma, Jimbo?"

Without the contrast between two or more different worlds, illustrated by Mike's reply, it would have to be in (this, actual, real) cruel world.

Indeed. Imagine the world (office, suburb, etc.) as a container. Use 'in' if something is within the container, and 'at' if something is just outside it or in its proximity.

Thanks for your replies, and what if a phrase "at the cruel world of violence" relates to a website devoted to or depicting this "cruel world of violence"? Does this leave me with using "at" if I call a website devoted to violence "a cruel world of violence"(a world on the pages of this website)? So in this case do I still view it as a container, or as a point on a line (a site in world-wide web)?

I think you could safely use either, but there may be other opinions.