text: what's the biggest city (as in size, not population) of the whole world? i always thought it was mexico city, but is it? the size not population. located 1829 km from brisbane, 883 km from townsville and 356 m above sea-level, mount isa proudly claims to be the largest city in the world; a fact born out by its accreditation in the guinness book of records. the argument is that the city extends for 40 977 sq. km, and that the road from mount isa to camooweal, a distance of 189 km, is the longest city road in the world.