For any and all of said purposes the board of supervisors may divide the county, or any area or areas within the county, into districts of such number, shape, and area as may be deemed best suited to carry out the purposes of this chapter; and within such districts it may regulate and restrict the erection, construction, reconstruction, alteration, repair, or use of buildings, structures or land.  All such regulations and restrictions shall be uniform for each class or kind of buildings throughout each district, but the regulations in one district may differ from those in other districts.