It is the purpose of this chapter to preserve the land, to promote the health, safety, morals and general welfare of the community and to lessen congestion in the streets, to secure safety from fire, flood, panic and other dangers, to provide adequate light and air, to prevent the overcrowding of land, to promote land conservation, to avoid undue concentration of population and to facilitate the adequate provision for transportation, water, sewerage, schools, parks and other public requirements.