Geography Reference
In-Depth Information
the field but it can also speed up the collection of
data, because surveyors do not have to determine
their location in relation to a map, which can be
difficult in areas without clear landmarks.
Moreover, GPS can help to relocate sample points
quickly and accurately so that resurvey can be
undertaken. The ability to record positional
information rapidly also enables more dynamic
systems and processes to be studied. GPS tracking
techniques have been used for a wide variety of
wildlife studies, for example to follow the
movement of organisms (e.g Moen
et al
. 1996).
which further change can be measured. In this
way, appropriate monitoring systems can be
established.
An example of work that illustrates how both
GIS and remote sensing can be used to establish
a baseline and to detect change is provided by
the various surveys of the British countryside
undertaken by the Institute of Terrestrial Ecology
(ITE) in the UK. Countryside Survey 1990
(CS1990), for example, was an expanded and
refined programme of work that built on two
earlier surveys in 1978 and 1984 (Barr
et al
.
1993). Collectively, these studies have provided
information on the stock and change of rural
land cover in Great Britain, together with data
on the changes in abundance of the more
common plant species that characterise the wider
countryside. The 1990 survey also set down a
baseline for the monitoring of freshwater biota
in rural areas.
GIS was used as a basic tool for the storage,
integration and analysis of countryside survey
data (Figure 40.6). The field survey component
of CS1990 mapped land cover, the character and
condition of linear landscape features and the
abundance of terrestrial plant species in a sample
of the 1×1 km grid squares from the Ordnance
Survey National Grid. The sample was stratified
by major landscape type, so that national
estimates could be made for each parameter
recorded. Of the 508 squares surveyed in 1990,
256 had been surveyed in 1984 and 1978, so
change could be determined. GIS was used as the
basic tool for this analysis. The field maps for
1984 and 1990, for example, were compared
using
overlay
procedures within the GIS. Thus
differences in the area of each land cover type
could be determined, or differences in the length
of linear features such as hedge-rows or walls
could be calculated. For the purposes of
dissemination, the summary data derived from
CS1990 has been set up on a simple GIS, known
as the Countryside Information System (Haines-
Young
et al
. 1994).
Since the 1990 survey was more extensive than
the earlier ones, CS1990 was regarded as the
baseline against which past change was calculated.
UNDERSTANDING OUR COMPUTER
WORLDS
In the first part of this chapter, we have looked at
some of the issues that surround the collection of
the information that we need in order to set up
our GIS. We must now consider how GIS can help
us to analyse these data to understand how the
environment might be changing, and what
importance we might attach to such changes. We
will use the framework set out in Figure 40.3 as
the basis for our discussion. On the one hand, we
will consider studies in which GIS has been used
to set up some baseline against which changes in
the overall condition of the environment can be
measured. On the other, we will consider the more
complex situation, when we need to consider
whether it is the dynamic behaviour of the system
itself that has changed for the better or worse. In
both cases, we are looking at the problem of
change
detection
.
Detecting changes in state
One of the easiest ways to detect change is in
relation to some baseline or initial set of
conditions. The baseline is used as a reference (or
control) against which differences in the condition
or
state
of the environment can be judged.
Although we may recognise that there is no 'time-
zero' or starting point, it is often possible to agree
that the state of the environment at some given
instant or period will stand as a reference against
