Example

Example

Considering rice-growing, the following conditions are assumed:

cultivation requires a lot of water, therefore the areas close to the hydrographic network will be privileged (use of the out-image data ``irrigable areas'');
cultivation is at relatively low altitudes (less than 300 meters) (using DEM) ;
for reasons of accessibility (by the man and the machines) and of productivity, the areas of rice-growing are close to roads and villages (use of ``distances to roads'' and ``distances to villages'').

These premises do not have the same importance:

first premise, expressing the presence of water, is most significant,
second premise, relating to altitude, is significant also, but with a less degree,
third premise, related to a factor of production, is the least significant of the three.

Production rule for rice-growing could then be expressed as follows:

if area favourable to rice-growing then always close to hydrographic network and principally altitude lower than 300 meters and only near to roads.

Each of the nine classes of vegetation of the area of Palni has its own production rule: table 1.

**Table 1:** Premises of each of the nine classes.
Class	Vegetation	Production rule
1	Low forest sempervirente	Only altitude higher than 1850 m. and tops of crests or bottoms of valleys.
2	Wet dense forest semi-deciduous	Only altitude between 900 and 1700 m. and plateau area.
3	Vallicole forest semi-deciduous	Mainly altitude between 500 and 1000 m. and plateau area.
4	Semi-deciduous forest or dry deciduous	Only altitude between 900 and 1800 m. and slopes of unspecified orientation, but abrupt (80%).
5	Wooded Savanna	Mainly altitude between 1000 and 1600 m. and medium slopes or tops crests.
6	Mosaic of savanna shrubby and deforestations	Only altitude higher than 1800 m. and plateau area.
7	Irrigated Cultures	Only altitude lower than 300 m. and irrigable area.
8	Dry cultures	Only altitude lower than 300 m. and close to roads.
9	Discontinuous thickets and pseudo-steppe	Mainly altitude lower than 300 m. and close to roads.

IRIT-UPS