This chapter is adopted for the purpose of defining, regulating and restricting the location, use, height, number of stories and size of buildings and other structures; the size of yards, courts and other open spaces; the density of population; the location and use of buildings, structures and land for trade, industry, residence or other purposes; creating zones for such purposes and establishing a Planning Board with powers to determine and vary the application of the regulations hereby established in harmony with their general purposes and intent; providing for the enforcement of the provisions herein and imposing penalties for their violation; all designed for one or more of the following purposes: to lessen congestion in the streets, secure safety from fire, panic and other dangers; to promote health, morals and the general welfare; to provide adequate light and air; to prevent the overcrowding of land or buildings; and to avoid undue concentration of population.