Between 1970 and 1972 Javier Carvajal built the facilities of the new Zoological Park of Madrid, referent of the Spanish architecture, in reinforced concrete. This communication aims to show some reflections, emerged after analyzing the 184 planes that the architect made for the Zoo of Madrid and which remained unpublished, in the General Archive of the University of Navarra. Thanks to the study of the original plans, we were able to approach the original project. The analysis of the different designs has helped us to understand the importance of drawing, in the genesis of the project. Geometry underlies the origin of all enclosures. The set could be understood as a system of systems, in which, as a collage, exist different compositional patterns that articulate the spaces that flow concatenated. The careful elaboration of the drawings, and the precision of their lines speak of the character of the architect, neat and rigorous; brilliant in the conception of the architectural space, and impeccable in its execution. Carvajal handled the control at any scale of all the elements of the project, and showed a great respect for Nature, which was to accommodate its more functional architecture.