Urban stock over time: spatial material stock analysis using 4d-GIS

A huge amount of construction material is required in urban areas for developing and maintaining buildings and infrastructure. Ageing stocks, which were built during a period of rapid growth in Japan (1955-1973), will cause a new waste flow in the near future. In order to assess urban metabolism with regard to building and infrastructure, it is necessary to understand change in its material accumulation both 'spatially' and 'temporally'. In this analysis, material accumulation over time is elucidated using four-dimensional Geographical Information Systems (4d-GIS) data at an urban scale. An approximately 8km2 urban area of Salford in Manchester, UK, and 11km2 of Wakayama City centre, Japan, were selected as case study sites. In this analysis, the material stock of buildings, roadways and railways was estimated locally over time, using a 4d-GIS database: (1) to find the spatial distribution of construction materials over time, (2) to estimate the demolition curve of buildings based on characteristics of an area, and (3) to clarify material accumulation with vertical location, such as above and below ground, from the viewpoint of recyclability. By estimation of the demolition curve, the life span of buildings in an urban area was found to be shorter than the national average respectively at both sites: 81 years in the urban area of Salford compared with 128 years for the UK; and 28 years in Wakayama City centre compared with the Japanese national average of 40 years. In 2004, 47% of total construction material was stocked in underground infrastructure in Wakayama City centre.