The height to width ratio of any space
generates spatial enclosure that is related
to the physiology of the human eye.
If the width of a public space is such
that the cone of vision encompasses
less street wall than sky opening, the
degree of spatial enclosure is slight.
The ratio of 1 increment of height to 6
of width is the absolute minimum if a
sense of spatial enclosure is to result.
As a general rule, the smaller the ratio is
the stronger the sense of place and,
oftentimes, the higher the real estate
value. Spatial enclosure is important on
all streets but is particularly important
for shopping streets that must compete
with shopping malls.
In the absence of opportunities to provide
spatial definition by building
facades, provision of disciplined tree
planting is an alternative. Trees aligned
for spatial enclosure are necessary on
thoroughfares that have substantial
front yards and setbacks.