<p>Life Cycle Assessments are generally confined to the assessment of products, in conformity with existing international standards. This frame requires defining a functional unit and allocation methods in order to attribute to the studied product its own environmental impacts. Although some attempts have been made to conduct LCAs of geographical areas, the methodological frame has not been really questioned and the definition of a functional units of a geographical area thus remains a challenge. I want to question the frame in the context of urban metabolism: why LCAs ? What for ? And how ? My presentation aims at showing why the current LCA frame is not adapted to face the challenges of industrial ecology, such as for example the analysis of strategies to implement circular economy systems in geographical context. It also wants to discuss the final utility of such approaches in order that they can be useful for actual decisions.</p>