447
The mountain area (M) occurs above 2100 m
with contour-lines close together, slopes
>5% with parallel drainage.
The slope area (S) ranges from between
1500-1800 to 2100 m, the general slope is
<5% with parallel drainage.
The escarpment area (E) ranges from 1800-
2100 m and is relatively flat with internal
drainage.
The plains (P) form the lowest elevation
category below 1500-1800 m, slope <2% and a
dendritic drainage pattern.
In the mountain, area and the slope area, the
altitude declines from NW-SE giving contour
patterns with a SW-NE trend. The slope area
has a very dissected appearance with the
streams flowing to the SE giving a striking
texture to the whole of this zone. The es
carpment, the eastern edge of the Gregory
Rift, is a distinct zone with an abrupt ele
vation change marked by clear fault lines
visible on the image. The plains in contrast
are flatter and characterized by much less
striking features. Vegetation is closely
associated with these zones and provides more
detail within these broad physiographic cate
gories.
For the landscape planner, this background
knowledge of the physiography, is of great
importance for constructing a viable plan.
Land-use and proposed land-use must be appro
priate to the whole bio-physical environment,
and in the case of Nairobi, this cannot be
properly understood without a perception of
the physiography. Related to the physio
graphic zones are variables such as climate,
vegetation and soils which control human
activity and ultimately establish land values,
3.2 Land-cover map 1:1M (Figure 4)
The checking of the map in the field provided
information on the location and character of
the identified boundaries. The upper and lo
wer boundaries of zone M, S,- E anti P could be-
verified, but other boundaries within these
zones were also visible. In some cases, the
boundaries are a transition between forest
and agriculture which is never very clear;
foresters cultivate crops and farmers grow
trees. Other boundaries between slopes (S)
and plains (P) are very clear where large
Table
2. Photo-tones
of the land
-coven map
Symbol
Phototone
Land cover
Location
M1
dark red,
red patches
forest
Aberdare Range
M2
red, light yellow
rangeland
forest
Ngong Hills
E
green mottled
rangeland
W of Nairobi
light yellow
yellow brown
red
bright red
built up
agriculture
forest
Limuru Road
S1
light red
light yellow
(small patches)
agriculture
N£ of Limuru
S2
green
agriculture
red mottled
yellow
built up
Kikuyu
Kiambu area
S3
bright red
Kahawa
green
agriculture
Ruiru
red mottled
yellow
black
built up
water bodies
Thika area
S4
bright red
pink
yellow (few spots)
agriculture
dairy
SE of Limuru
S5
brownish red
built up
Nairobi
yellow/brown
blue (few spots)
agriculture
range land
forest
Ngong area
P1
yellow brown
blue/brown/green
rangeland
Athi Plains
P2
bright blue
yellow/brown
(small patches)
built up
Nairobi
P3
green/yellow
bright red
brown
rangeland
agriculture
between
Nairobi and Thika
P4
brown agriculture
bright red
yellow/brown rangeland
(all' in small patches)
01 Donyo Sabuk
Ruiru area
Figure 4. Land-cover map.
scale irrigated coffee plantations have been
established. Informal settlements at the out
skirts of Nairobi City, small scale farms and
pastoral settlements form a transition and
not a sharp line. The escarpment area (E) is
more clearly delineated by the geographical
features producing differences in physio
graphic characteristics.
These variations in vegetation and land-
use visible on the satellite image, led to
the realization that the original four ?ones
could be further sub-divided into nine land-
cover zones, based on differences in texture
and tone (Table 2)
In the mountain area (M) two zones were
distinguished. M1, on the slope of the Aber-
dares, this is a zone of forest plantations
and mixed indigenous forest. M2, the Ngong
Hills, which is a zone of grasslands with
small forest remnants (Photo 1 and 2).