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).