Find in an area

[Yazrihm]

Hi,
I'm trying to find an entity in a specific area exemple.40x40 around an entity.
A screenshot :
[IMG]http://image.prntscr.com/image/75a7a9a89ec440f39d4aa2f432e87cce.png[/IMG]

But don't know how to trace the area and search into if you can just give a function or anything else.

Thanks, Yazrihm.