80 
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.