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Braking down the problem
The problem must be braked into smaller and smaller pieces, until the required data and steps to solve the problem are known. These steps are objectives that will be solved to measure the suitability of each location. A consideration in defining these objectives is that they must be something measurable. How is it possible to measure what is the optimal site for the lakes and path for the channel? Suitable areas must be at the low levels to be economic in digging, the successful lakes is that near to the cities to archive its aims, and good path of channel is that the shortest. So, the three objectives are answering for "where are the low-level areas? Are these areas near enough to the cities? Where is the short path of the channel? These objectives become data layers or themes.

Where are the low-level areas?
To create a map of suitable elevation areas, some characteristics of low-level areas must be defined using analysis of grid theme of the whole area. From a data set of the area the low-level areas can be selected, ranked map of these area can be created, and compare this with real-estate data to evaluate the result of ranked map. From this evaluation result the suitable elevation areas can be defined.

Data set of area: - DTED is downloaded data represents the elevation value in meters unit for each square cell. This cell is the smaller measurable unite. The cell's size depends on the resolution of the raster image and the available detailed data. The used data contain cells have square size 29.808 second. Single value is store for each cell. This value indicates to the average elevation level of the cell.

Low-level areas: - using query builder tool the low-level cells can be selected with a logical expression such as ([Value] < 0) will select every cell have value less than 0. This is understood that the selected area is the under Sea-level areas. 

Ranked map: - The legend type, classification type, numbers of classes, classification field, classes label, and color ramps can be specified using legend editor tool. Specifying these parameters will define the raked map from low to high level of land.

Real-state data: - it can be optioned from field survey or some stored data such as paper maps for landmarks such as depression, hill, or geodetic point. In this study the paper maps of partial area which contain some of these landmarks are available.

Evaluate of ranked map: - the map must be evaluated to insure the accuracy of data. The evaluation can be done by comparison of some samples from the real state with the same position in the ranked map. The successful sample must be leave as the same state and the unsuccessful sample can be corrected using the Editing toll or it can be removed and ignored. 

Suitable Elevations areas: - from the legend of ranked map the elevations are shown from the most low-level areas to the most high-level areas. The cell value of the sea is equal 0, the cell of elevations over the sea level is ranged between 1 - 2447 meter, and the cell of the under sea level is ranged between -32766 to -32382. So the suitable area for lakes must be negative elevation and less than 85 meter. The negative values has been reclassified to one range called "under sea level"

Are these areas near enough to the cities?
The design of separate urban elements to support urban tourism and recreation activities has long a long tradition in the urban environment (Bendict Dellaert, 1995). In many cases cultural and monumental urban setting have been preserved to be enjoyed by both residents and tourist. (Wylson A. and P. Wylson, 1994) The urban environment in its totality in many cities supplements the perception and use of the separate urban elements (Ashworth G. J., 1991). So, that is the proposed tourist facilities must do duplicate function in both of urban and tourist society. (Jansen-Verbeke M., 1988) This directs the decision of site-selection to necessarily to be near enough to the city. Therefor, the fit site of proposed lakes must be far maximum 10 km form the centers cities. So a map showing the areas within 10 km of each city in EWDA must be created using the Find Distance function of ArcView GIS.

Where is the suitable path of the channel?
The best path of channel is that located in the short path and has small number of dropped slopes from low-level to high-level in the water flowing direction. In another words, the path, which located in middle elevation between maximum and minimum level, in this case the suitable elevation is that has value 180 m. The middle level map is created using the logical expression ([Elevation] < 180).

The diagram of the model shows the start of process is to statement of the problem, then breaking down the problem to find the objectives, and assigning value to the objective to ranking the value from the best to the worst of each theme. The last step is to create the composite suitability map of the locations for the proposed lakes by combine the suitability maps of each objective: map of area level, map of far area, and map of length path.


Fig. (1) shows the diagram of modeling process.


Assigning value to the objective
After creating the suitability maps of the three objectives, the numeric values must be assigned to classes within each map. 

Ranking the values of elevation surface
Using legend editor of the Elevation theme, the classification type has been specified as Natural Breaks to looking for groupings and patterns inherent in the data with minimizing the variation within each class. The number of classes has been specified as 66 class the lowest class describes the under Sea level, the zero value class describes the Sea Level, and the another 64 classes are divided into 64 ranges of elevations.

Ranking the values of distant map
The map unit of the elevation's theme is Decimal Degree, so the distant-map unit is created in Decimal Degree. Using the Find distance function the continuous map of distance from EWDC (Kharga, Mute, Farafra, Bawity, and Siwa) and the coastal cities Alexandria and Matrouh is created. This map is called Distance to cities and automatically ranked into 13 classes with value according to the distance between cities. The decimal degree equal 103 Km, therefor, the 1 km must be considered as 1/ 103 or 0.0097 of map unit.

Ranking the path map
The map of middle elevation level is created by the theme of suitability Path that created as line features according the levels under 180 meter, each feature has value of path length in the length field of attribute table. By using legend editor of this theme and specifying the legend type as Unique Value, the path map will be ranked into unique class for each feature. Then the distance maps to each path are created using the find distance function for each path. These maps called Distance to estimated Path # 1, Distance to estimated path # 2, and Distance to estimated path # 3.

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