Repurposing is an initiative that considers the reuse of built places, structures, and facilities that no longer serve new populations and economic initiatives that have replaced an earlier demographic or economy. In many cases repurposing will require retroﬁtting older facilities that no longer serve the needs of new users with new designs to accommodate the new uses or programming changes. Retroﬁtting with new designs may also be necessary to address changing environmental conditions such as rising sea levels or increased threats from ﬂooding conditions in a region. Building retroﬁtting could include elevating structures or modifying the grounds to increase their water-holding capacity in the form of detention ponds or redirecting storm water to safer locations (such as wetlands, if they exist). Examples of facilities that may need to be retroﬁtted due to changing demographics include parks, commercial and industrial areas, and street landscapes. Adaptive reuse is the converting of structures or spaces for new uses of derelict and even abandoned buildings, such as commercial malls and whole districts, such as warehouses and industrial sites. Warehouse districts, because of their desirable close proximity to urban centers, are being converted into highly desirable and valued living and commercial space. Railroad rights-of-way no longer in use are being converted to walking trails and bicycle routes. Industrial zones have been converted to other purposes such as the industrial area of North London that was converted ﬁrst as the venue for the London 2012 Olympics. Subsequently the same Olympic site was repurposed for outdoor recreation, new housing, and commercial uses.