To grant, upon appeal or petition, with respect to particular land
or structures or to an existing building thereon, a variance from
the terms of this bylaw where, owing to circumstances relating to
the soil conditions, shape or topography of such land or structures
and owing to conditions especially affecting such parcel or such building
but not affecting generally the zoning district in which it is located,
a literal enforcement of the provisions of this bylaw would involve
substantial hardship, financial or otherwise, to the appellant, and
where desirable relief may be granted without substantial detriment
to the public good and without nullifying or substantially derogating
from the intent or purpose of this bylaw. The Board of Appeals shall
not grant use variances.