Desiccation cracking of soils is of great importance to geotechnical and geoenvironmental engineering as it affects the soil physical integrity. Yet the mechanisms of drying cracking in soils, and the ways to control or avoid it, are still elusive. This paper aims at offering a better understanding of the factors that control the desiccation crack pattern characteristics in soils at the macro-scale. An experimental program is first presented. It consists of the drying of clayey silt slabs, constrained at the bottom and the measuring of the geometrical characteristics of the one- and two-dimensional crack patterns obtained. Then the way desiccation crack spacing and geometry can be predicted is dealt with. It is discussed to which extend the initiation location of successive cracks can be deduced from the form of the stress field. Calculations of the overall energy of the system are further used to derive an estimate of the desiccation crack spacing. An assessment of the obtained desiccation crack spacing value is proposed.