The interfacial problematics of the City layer include both the micropolities configured by architectural envelopes and the equally complex virtual envelopes that organize mobile Users as they meander past the gathering confines of any single building form. Like the hard envelopes Zaera-Polo describes, software envelopes are also sites of convergence between function and representation, linking program and figuration, and so design of the City layer (and the programmatic envelope in particular) draws from architectonic and urban formats alike, but no more so than from the diverse media of planetary-scale computation. The mutual economy of software and architecture is one of programmatic drift, but the interfaciality of software is of particular interest for The Stack in large part because, as said, software is now asked to structure flows of social organization that had once been the assignment of architecture in the modern era. For the moment, hard-into-soft is the more trafficked direction of programmatic transposition between the two, though that may reverse in unexpected ways. While the virtual envelope may be amorphous and invisible, it is not structureless or infinitely permeable. Software envelopes also conform into typological envelopes, sometimes even in the manner described by Zaera-Polo, and according to their own spatial politics, they can straddle the material and the immaterial, variously enforcing, augmenting, or negating the hard architectural envelopes he describes. As physical and virtual envelopes overlap, the clarity of a singular sharply defined exterior is less certain; hard and soft interfaces leak information into one another through their perforated skins. This suggests a need not only for a parallel typology of software envelopes individual performances, but also for a composite matrix describing the differing ways that physical architectural and virtual software envelopes interweave within the other to form the hybrid platform apparatus that in turn produces the subjects and polities of the City layer. <sup>33</sup>
City Layer
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