Starting up; early stages - Introduction to Environmental Impact Assessment - page 117

is no negative significance. This distinction between magnitude and significance is
important: an impact could be large but insignificant, or small but significant. For
instance, in ecological terms, paving over a large field of intensively used farmland may
be quite insignificant compared with the destruction of even a small area of an SSSI.
The Leopold matrix is easily understood, can be applied to a wide range of
developments, and is reasonably comprehensive for first-order, direct impacts. However,
it has disadvantages. The fact that it was designed for use on many different types of
project makes it unwieldy for use on any one project. It cannot reveal indirect effects of
developments: like checklists and most other matrices, it does not relate environmental
components to one another, so the complex interactions between ecosystem components
that lead to indirect impacts are not assessed. The inclusion
P roject action Environmental

component

Construction Operation

Utilities Residential and

commercial
buildings

Residential
buildings

Commercial
buildings

Parks
and open
spaces

Soil and geology • •

Flora • ● ○

Fauna • • ◦

Air quality •

Water quality ○ • •

Population density ◦

Employment ○ ○

Traffic • • • ●

Housing ○

Community
structure

• ○ ◦

•=small negative impact ◦ = small positive impact

●=large negative impact ○=large positive impact

Figure 4.11 Part of a magnitude
matrix.

of magnitude/significance scores has additional drawbacks: it gives no indication whether
the data on which these values are based are qualitative or quantitative; it does not
specify the probability of an impact occurring; it excludes details of the techniques used
to predict impacts; and the scoring system is inherently subjective and open to bias.
People may also attempt to add the numerical values to produce a composite value for the
development's impacts and compare this with that for other developments; this should