In this paper, we introduce a layout description and generation model, GBLD, based on the notions and elements of L-systems and context-free grammars. Our layout model is compatible with geometric layout formats, such as GDSII or CIF. However, it is more powerful and more concise. The layouts represented by GBLD are sizeable, parameterised, and can incorporate design rules. GBLD has the potential to be used as a format for analog layout templates, analog layout retargeting, as well as the final layout format.