Daoud Brikci, Hichem 
  
3 PRACTICAL PROBLEMS 
The main factors of the agricultural development is irrigation. Taking into account of the importance of agriculture and 
food-invoice, scientists constantly look for new soils able to be irrigated and then apply a policy of management. This 
study requires a multidisciplinary approach involving topography, pedology, geology, geomorphology, agronomy, 
ecology, economy.,... 
The study area is situated at 20 km from Maghnia and 150 km from Oran. It represents the Northwest extension of the 
plain of Maghnia along the borders between Algeria and Morocco. This area is called Zriga; it is 420m higher and is 
bordered to the north by Beni Snassen, to the east by the plain of Maghnia, to the south by the plain of Angads 
(Morocco) and to west by the borders between Algeria and Morocco. 
In this study, we have to determine a map illustrating three categories: 
e category 1: irrigation suitable land, 
e category 2: fairly suitable land, 
e category 3: not suitable land. 
This is based on the six following criteria: 
e proximity to habitations, 
° to roads, 
° to wells, 
° to hydrographic network, 
e slope, 
e soils types. 
The objective, hence, is to illustrate how the integration of ELECTRE methods into a GIS does 
contribute in land suitability evaluation. 
First of all, we process the "classical" procedure then we apply ELECTRE approach. The images 
showing proximity to roads and hydrographic network were created by rasterizing the roads and 
hydrographic vectors and then running DISTANCE. The image illustrating the proximity to 
habitations and wells were created by using the cost module using the COSTGROW algorithm. 
Running SURFACE on a digital elevation model for the study area, the image representing the slope 
factor was created. The land cover was obtained from the pedologic map 1/25000. The main types of 
soils are: 
isohumic, 
calcimagnesic, 
immature alluvial deposited, 
unweathered mineral alluvial deposited, 
fersiallitic. 
3.1 Idrisi Approach 
Each of these images expresses the basic nature of the factors identified in this study. However, using 
the weighted linear combination procedure (MCE module), the factor maps should be standardised to a 
consistent range of byte binary integers. In addition, it requires that each be constructed such that 
higher values indicate areas that are more suitable on that factor. 
To develop a set of weights for the factors such that they add up to 1, the pairwise comparison method 
was used (Saaty's technique, WEIGHT module). Weights can be derived by taking the principal eigenvector of a 
square reciprocal matrix of pairwise comparisons between the criteria. The comparison concern the relative importance 
of the two criteria involved in determining suitability for the stated objective. Ratings are provided on a 9-point 
continuous scale [1(equal), 3 (moderate), 5 (strong), 7 (very strong), 9 (extreme)]. 
  
308 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.