The purpose of this chapter shall be to promote the health, safety, morals and general welfare of the community; to lessen congestion in the streets; to secure safety from fire, panic and other dangers; to provide adequate light and air; to prevent the overcrowding of land; to avoid concentration of population; and to facilitate the adequate provision of transportation, water, sewerage, schools, parks and other public requirements. The size of buildings and other structures, the percentage of lot that may be occupied, the size of yards, the density of population and the use of buildings, structures and land for trade, industry, residence or other purposes are hereby restricted and regulated as hereinafter provided.