Vary the application of the regulations herein established and establish appropriate requirements for lots less than the required area, in any district, existing at the effective date of this chapter, lots of exceptional topography, lots bordering upon the shoreline of the Village or lots of irregular shape having small frontage on any street and, in cases embraced within this subsection, the Board may determine for the purposes of this chapter, which of the open spaces shall be considered as the front yard, the side yards and the rear yard and, with respect to lots bordering upon the shoreline, the mean high-water line shall, for such purposes, be considered to be the property line of the lot.