Which city design approach combines architecture and ecology, proposed by Paolo Soleri?

The concept of "Arcology," introduced by Paolo Soleri, effectively merges architecture with ecology to create self-sustaining urban environments. This approach emphasizes the design of cities that are densely populated and resource-efficient, promoting coexistence with the natural environment rather than its degradation.

Arcology aims to minimize the ecological footprint of urban living by integrating buildings with natural systems. This involves innovative structures that serve multiple functions, reduce resource consumption, and facilitate social interaction, all while reducing reliance on cars and promoting walkable communities. The overarching goal is to create urban habitats that support both human and ecological systems holistically.

In contrast, the other approaches mentioned do not encapsulate this vision as effectively. A floating city generally focuses on an architectural response to rising sea levels, lacking the integrated ecological aspects defined in Arcology. A megalopolis refers to a large, sprawling urban area often characterized by urban sprawl and may not prioritize sustainability or ecological integration. The neighbourhood unit concept focuses on social interaction and community layout without blending architecture and ecology in the distinct way Arcology does.

Thus, the essence of Arcology is its dual commitment to architectural innovation and ecological stewardship, making it the correct choice in this context.