"Yard, Rear" means a yard extending across the rear of the lot between the side lot lines. In the case of Through Lots there shall be no rear yard. On all other lots the rear yard shall be at opposite ends of the lot from the front yard.
Depth of required rear yards shall be measured at right angles to a straight line joining the rearmost points of the side lot lines. The forward rear yard line of a required rear yard shall be parallel to the straight line so established. When a lot is adjacent to an alley the required rear yard may be measured from the center of the alley, and one-half of the alley width may be considered a portion of the required rear yard.