I.e.if you want a trigger that converts ulfsarks from player 1 to player 2 when they are near a temple,the Units In Area is the appropriate condition to use.
Now,what might not be known is that with a very simple "trick" the An example would be the best way to describe this... With this condition the effect will be fired whenever player 1 owns a siege camp on any spot of the map. P.S.If you have problems understanding the Units In Area condition,check this usefull thread:
This means that the specified area will cover the whole map,so the effect will fire whenever the number of the specified by the designer units exist on the map.
Say you want a trigger that alerts player 2 when player 1 has built a siege camp,so that say the first will then start a counderattack.You should then use the Units In Area Condition like this:
Anything you want...