In order to classify, regulate and restrict the location of trades and industries, and the location of buildings designed for specified uses, to regulate and limit the height and bulk of buildings hereafter erected or altered; to regulate and limit the intensity of the use of lot areas, and to regulate and determine the area of yards, courts, and other open spaces within and surrounding such buildings, the City is hereby divided into six classes of districts. The use, height and area regulations are uniform in each class of district and said districts shall be known as: