“Urban development” means, for purposes of Article 6, Division 6, “Annexations”, the construction on land of improvements for residential, institutional, commercial, industrial, transportation, public flood control, and recreation and similar uses, in contrast to the use of the land for growing crops, truck gardening, grazing of farm animals and other agricultural pursuits. The term also applies to vacant ground which has been or is being prepared for urban development by such steps as subdivision into lots or plots and blocks, installation of water and sewer lines, construction of access streets, and construction of railroad spur or branch tracks.