Geographical and environmental conditions were two of the most important factors on the design and construction of traditional architecture. Traditional earthen architecture is found throughout the Iberian Peninsula in numerous constructive techniques and variants, most notably rammed-earth, adobe and half-timber. The varied morphology, climate, geology and culture of the Iberian Peninsula, together with its immediate surroundings, have a direct effect on the development and the properties of traditional architecture. Thus, the objective of this research is to establish the relationship between the geographical characteristics and the distribution of the earthen techniques. For that purpose, the authors of this text have carried out a thorough data collection throughout the whole of the Iberian Peninsula in order to identify the main characteristics of this architecture in each location and to produce maps featuring the locations for each technique. This mapping of numerous techniques has been compared with other thematic maps of the territory, establishing relationships between the different techniques and specific properties of a given area. These provide hypotheses on which factors encourage or hinder the use of earthen construction techniques. Moreover, the relationship of traditional architecture with geographical factors and its specific morphology on a given place has provided many design lessons for a sustainable architecture. Those lessons must be taken into account on rehabilitation works and new architecture.