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automatically, may be considered to be a good and easy way to solve the
problem, but in tests^ it turned out to be very difficult to separate
shadows without any vegetation from dark parts of vegetation by means
of densitometry.
The number of existing trees and the portion of green within
defined parts of a city may have some special interest for local experts
in this field, but this type of information has neither a general mean
ing nor is it ready for comparison purposes. Based on the assumption,
that all urban vegetation does exist exclusively to support the welfare
and life-quality of the population and to serve for recreation, the
value of vegetation depends upon the number of people who enjoy its
benefits. That is why the ratio between the number of trees and the
number of people or the ratio of green area to the population in the
respective area is supposed to be a good expression for the importance
of the existing vegetation. The figures obtained from photo interpre
tation were therefore converted to the information ’’inhabitants per
tree” and "square metres green area per inhabitant” using the results
of the census 1970 (FABRICIUS, 1973). The expression ’’inhabitant” is
defined differently. From the statistical report of Freiburg the term
’’total number of persons who make use of the respective unit” was
chosen for the calculations. These figures include for each statistical
block the residents ("night population”) and the number of persons, who
work in the block, but do not live there. Not included in this figure
are temporarily present people such as visitors of businesses or public
offices; they, too, to a certain extent, should be counted as people
enjoying the benefits of urban vegetation. Even without including
visitors the resulting code-indices show, that in some parts of the
city, though away from downtown areas, more than 100 or even more than
200 people could assemble around each existing tree. There are numerous
people, for whom in their normal vicinity not more of a vegetation-cover
is available than the size of a blanket — all green spots like railway-
dams, backyard-green, roadside trees etc. included.
The statistical blocks which are shown in figure 1, figure 2 and
4 show the amounts for the terms "inhabitants per tree" and "m 2 green
area for each person”. These units are too small to show any signifi
cant differences of local life quality, because it is definitely not
necessary (though desirable) to have green zones in each block. But
for planning purposes information concerning the smallest units can
be very valuable, because these detailed data show mainstays of develop
ment very clearly. Figure 3 and figure 5 show the same information
as figure 2 and figure 4, but combined to the next larger units, the
statistical districts. The more distinct differences within the city
are shown here as well, and even more clearly and as a valid reference
for a deficiency of life-quality. An area of missing vegetation,
1)
Tests were carried out by Dr. HELBIG — compare his paper in these proceedings.