Site Selection for Network Expansion

Introduction

This example illustrates the choice of a site to expand the fiber optics network of a telecom company. The company has already a certain optical coverage of its territory and needs to decide where to expand.

Those sites are evaluated while considering six different criteria:

The cost of the construction site expressed in euros.
The delay of the work expressed in days.
The impact of the expansion on the company’s image.
The annual revenues that will be generated by this expansion.
The constraints related to the construction site. A note has been established by an engineering study taking into account operational and legal constraints (the lower the better).
The proximity of the next site with the existing network.

The sites represent the different possible alternatives. They are listed in the Alternatives tab of the start interface (Figure 1). The criteria are listed in the Criteria Tab as shown in Figure 2.

Figure 1 - Click to enlarge

Figure 2 - Click to enlarge

The Evaluation tab, represented in Figure 3, is a grid that contains an alternative in each row and the criteria in each column. Basically, the values in that table represent the performances of the sites for each of the criteria.

Figure 3 - Click to enlarge

Figure 4 - Click to enlarge

Analysis

Figure 5 - Click to enlarge

By going into the menu Analysis -> Visualization -> Global Visual Analysis (or CTRL + G), you open a visual representation of the situation. The sites are represented by the points while the criteria are represented by the axes.

If an alternative goes far in the direction of an axis (click on the axis extremity to display the projections), that means it performs well on the given criterion. For instance (see Figure 5), the Site E is the best regarding the delay (i.e. the lower delay) and is followed by the Site C. On the other hand, the Site E is not so good on the impact criterion. The Site C and F are the best for this criterion as it can be seen in Figure 6.

If two axes go in the same direction (and are close to each other) that means that the related criteria are correlated. On the other hand, if two axes go in two opposite directions, it means that the related criteria are anti-correlated / in conflict. This is easily observed for the revenues and the proximity that go in opposite direction. This means that in average and for this specific set of sites, the most profitable sites are the most distant from the existing network. Let’s emphasize that the configuration only depends of the datas. Let us note that the cost and the delay go in the same direction, meaning that the sites having high construction costs require long delays.

The red axis (the one without label) represents the so-called “decision stick”. It represents the direction of the most preferred site. Indeed, it is computed with the weights given by the company and represents the compromise it wants to make among the different criteria. Projecting the site on this axis (right click on the chart then click on “Stick projections”) will thus give a visual representation of the ranking as shown in Figure 7. The most preferred sites are the Site E and the Site C.

Figure 6 - Click to enlarge

Figure 7 - Click to enlarge

Let’s open the Global (numerical) ranking by going in into the menu Analysis -> Ranking and click on the Ranking menu item. We do now have the numerical confirmation. The most preferred site is the Site C with a score of 0.28 followed by Site E with a score of 0.25 as represented in Figure 8.

Figure 8 - Click to enlarge

Figure 9 - Click to enlarge

Let’s open the stability intervals tools (Analysis -> Sensitivity -> Stability Intervals). They indicate, for each criterion, in which interval the weight can be changed without affecting the ranking. For instance, you can see that the cost (which is weighted to 16%) can be changed from 0% to 23.1% without changing the first ranked site. We can check it in real time by opening the walking weights (Analysis -> Sensitivity -> Walking Weights or CTRL + W). You can put it in the left part on the main window by drag and dopping it. When the Walking Weights tab is open, you will see the three categories (financial, logistics and image) in the chart. To work with the sub-criterion, select Absolute in the lower left part of the panel (under the slider). You can now select the cost criterion in the tree and move the slider to 24%. For this new weight value, the Site E comes first in the ranking as more importance is now given to the cost. On the other hand lower the cost importance and you will see that it the Site C will remain in first position.