The range of area effects is indicated by the color of the effect icon.
Blue: Effect that activates in that area.
Purple: Effect received from adjacent ally-controlled areas.
Green: Effect that is applied to adjacent areas after seizing that area.
Tap the icon when selecting an area to see what the effects are before heading into battle. Here are some typical area effects to help you out.
Infantry units in your army gain Atk/Spd/Def/Res+4.
Armored units in your army gain +1 movement range at the start of the turn. (Effect active for one turn only. Does not stack.)
Cavalry units in your army are guaranteed to perform follow-up attacks when initiating combat.
Allies can move to a space adjacent to a flying ally within two spaces.
Get the advantage in battle by preparing teams that focus on the unit types (flying units, armored units, etc.) targeted by area effects ahead of time.