gives a better connection between the different peaks.
It is important to mention that the absolute values of the iso-
pollutes are estimates calculated from a linear interpolation
between the observations, and should be commented carefully.
This map proved to be very useful for the selection of "hot
zones" which have to be studied more in detail. Thus it was
possible to relate the peaks on the left side of the map to
dense traffic nodes. The non-linear surface using Krumbein's
expected-value method (fig.4) generalizes the situation,
showing as main directions one NE to SW and three parallel
axis standing perpendicular on the first one (fig.4a). The
residuals have a more meaningful pattern (fig.4b) and show
clearly the screening effect of the tree-plantation along the
edge of the industrial zone. The linear trend surface analysis
(fig.3a) generalizes even more. The pattern of the residuals
(fig.3b) is essentially similar to that of the isopollutes.
Finally, the potential surface (fig.5) gives the most abstract
pattern, showing a dome centered on the NE-side of the factory.
The second example illustrates the geographical inter-
pretation of the isopleth map (fig.6) of a chemical plant along
the estuary of the Scheldt near the town Terneuzen (the Nether-
lands). The map of the isopollutes shows a complex pattern of
elongated "ridges" and the relation with the industrial area is
not evident. Comparison of this map with the soil map and the
land use map was carried out, as well as a field investigation
for each "hot zone". Only the "peak" A seemed directly caused
by the industry. The ridge B along the channel Ghent-Terneuzen,
near the sea sluice, is caused by the infiltration of heavily
polluted water into the soil. The ridge C is related to an old
creek where the ecological conditions are connected closely
with drainage conditions, and so far no evidence was found to
indicate air pollution as a cause of damage. The ridges D and
E correspond with plantation of poplar on dikes which are about
2,5 m high. Wind damage, particular soil conditions and cattle
grazing cause important physical damage of the trees.
