So a point of clarification: when you say "art" do you mean literally art or simply visual representations, i.e. maps? It's true that the distinction between an artistic depiction of a place and a true map can be vague in antiquity and the Middle Ages, but the two are definitely different questions that require different approaches. The former in particular suggests the implicit belief that true maps did not exist in the Roman world, of which notion at the very least I may disabuse you (provided you actually have it and I'm not just reading this wrong) without knowing more. The Severan Forma Urbis, probably based on an earlier Flavian map, was a highly accurate map of the city publicly displayed. Other cities and municipalities had city maps, drawn up mostly for land surveying purposes, quite early, and it's almost certain that there were Republican and early Imperial maps of the city that well predate the Flavian Forma Urbis, which unlike its Severan successor we do not have. Is that what you're asking for or are you asking about actual art?