It does illustrate the workings and rationale underlying a GIS in operation. The problem is identifying the best areas for planting a specific crop within a valley along the north side of the Senegal River at the border between Mauritania and Senegal, two West African nations along the Atlantic Ocean. The cereal crop is sorghum, a tall grass cultivated in tropical climates that yields grains suited as silage and fodder or, in some varieties, a cane sugar-like juice called sorgo. The first factor is the elevation variations or relief. The river is the lowest part of the scene, yet it appears to back up against the medium green pattern.
Gentle hills occur in the west and northeast sections.
This depression controls the location and retention of water during floods that take place routinely during the rainy season. During this stage, the soil types in the region differentially absorb floodwaters, such that, some retain enough over the long term to provide a continuing supply of moisture during the growing season. Thus, soil type is another critical factor. The black areas are not considered further, for other reasons. Again, we require binary logic using Boolean algebra.