The slopes were classed or grouped depending on the rank that each crop requires this was done based on available literature. The detail slope class of
each crop can be seen in appendix.
3. Generated Temperature Map
Temperature data were required to determine the distribution of temperature area. The temperature data was estimated using a formula with the
input of altitude polygon derived from altitude of topographic data. Same with soil and altitude, plant need certain temperature condition to grow optimally. The
formula that is used to estimate the temperature data is the Braak formula, and
the equation is given below: T = 26.3 °C – 0.01 altitude in meters 0.6 °C
Contour Data Temperature Map
Braak Formula
Figure 3.5. Generating Temperature Map In this case, temperatures were divided into 3 classes, based on the
limitation of the temperature that can influence to the growth of plants.
4. Soil Map Digitizing Process
Soil type data that was obtained from Puslittanak was a paper map. For further process is needed to change the format of soil type data from hardcopy
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data to digital. This process can be done by digitizing the paper map with Autodesk Map 5 application, and then the digital data result will used for
analyzing process by using ArcGIS 9.
Figure 3.6. Digitizing Soil Map Digitized
5. Generated Rainfall Map
Rainfall map of investigated area was generated from digitized process of rainfall map which was obtained from Puslittanak Bogor. Digitalizing process
was carried out by using Autodesk Map 5 and the result was used for next spatial analyzing process.
Figure 3.7. Digitalizing Rainfall Map Digitalized
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3.3.3. Spatial Processing and Analysis
1. Modeling Approach
There were several criteria involved to determine the growth factor. Multiple criteria typically, have varying importance; each criterion can be
assigned to a specific weight that reflects how big each criterion influence to the plant growth relative to other criteria. The principle of weighted method is to give
value to each factor, which influence to the land suitability for crops growth. The value of factor can be divided into two kinds of value, they are environmental
factor value and human value. The environment factors consist of soil type, water availability, slope, and temperature.
Each crop, which will be investigated in this research, has its own growth requirement. Optimum growth of crop could be reached if the requirements are
met. Based on crop tolerance to the environmental value, the degree of suitability can be divided into 4 classes: highly suitable, suitable, marginally suitable, and
not suitable. While the environment factor value depend on the condition of the
environment, which meet to the optimum growth of crops; the human factors, which contribute to the assessment of environment factors, are obtained from the
questioners that are distributed to experts. The expert in this case consists of policy makers, farmers, and researcher, which have experience or expertise on the
land suitability for each investigated crop. The human factor values are set from 0 up to 100 percent. The human factor values applied to each crop is described in
Table 3.2.
26 Table 3.2. The human factor value from expert for Environmental factors
Crops Slope
Water Availability
Soil Temperature
Total Rice 25 30
29 16 100
Corn 28 23 31
18 100 Soybean 28
22 33
17 100
Peanut 27 24
32 17
100 Mungbean 26
22 33
19 100
Source: Respondent data After getting the result of human factors values from respondents above, the
weighting method will process all data with the formula that have created. The formula describes the relationship between all factors i.e. environmental factor
and human factor in weighted method analysis. As mentioned before, there are two values for the overlay processed of
weighted method i.e. value for each environmental factor altitude, water availability, soil, and temperature, which were given by experts above, and value
for the class of each environmental factor that depend on literature. For instance, the values of overlay weighted method for corn are shown in Table 3.3.
Table 3.3. Factor and Class value of Overlay Weighted Method
Factor Weight value
Class of factor Class Value
Total Value
Slope 28
8 8 – 16
16 - 30 3
2 1
84
Water Availability
23 500 – 1,200 mm
1,200 – 1,600 mm 1,600 mm
3 2
1 46
Soil type 31 Very
suitable Suitable
Marginal Suitable 3
2 1
93
Temperature 18
20° - 26° C 26° - 30° C
16° - 20° C 3
2 1
36 Total 100
259
27 Note:
factor value : from expert Class of environment factor : from literature
class value : 1= marginally suitable, 2 = suitable, 3 = highly suitable
The land suitability value is summing up of all factor total values that were applied, and the total value itself is obtained from human factor value multiplied
by the environment class value. The minimum and maximum values of land suitability can be calculated as:
a The maximum value: if all factors have maximum class value. The maximum value: 100 3 = 300
b The minimum value: if all factors have minimum class value. The minimum value: 100 1 = 100
As mentioned before, the land suitability areas were divided into 3 classes that are very suitable, suitable, and marginal suitable. Therefore, the range value
between land suitability classes is the maximum value minus minimum value divided by number of classes. So, the range value is 300 - 100 3 = 66.67, or
rounded up to 67. The interval values for each class are: -
Marginally suitable area having value between 100 up to 167; -
Suitable area having value between 168 up to 235; and -
Highly suitable area having value between 236 up to 300. If one or more factors or classes have 0 zero value, the result becomes a
not suitable areas.
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2. Revenue Cost Analysis Approach
