The document discusses cities as interfaces between human social and economic activity and computational systems. It notes that data will create more connected cities and is critical to their sustainable success. It also discusses how the feedback loops between different data types and physical experiences are becoming more symbiotic. The interface between public and private infrastructure and personal systems is key to consider the appropriate level of presence for these interfaces. The document advocates for designing technological experiences in cities to support and enhance the "flow" of human enterprise in cities.