Sentence:  Since the mid-1980s, when Indonesia first began to clear its bountiful forests on an industrial scale in favour of lucrative palm-oil plantations, “haze” has become an almost annual occurrence in South-East Asia. The cheapest way to clear logged woodland is to burn it, producing an acrid cloud of foul white smoke that, carried by the wind, can cover hundreds, or even thousands, of <WSD>square miles</WSD>. 
Meaning of the word marked with <WSD> tags:  A unit of area ("abbreviation" '''sq mi''' "or" '''sq. mi.''' "or" '''mi2''') equal to the area of a square the sides of which are each one mile long.