What kind of book is Invisible City in Calvino's novels?

Invisible City is a novel about Kyle Poirot telling Kublai Khan about the city, or an allegorical essay about the concept city. It is the last love poem that Calvino wrote for the city when life in the city became more and more difficult. The book depicts various cities: the city of memory, the city of desire, the city of continuity, the city of symbols, the city of trade, the city of death, the city of concealment and so on. In the end, Kublai Khan found that all the cities described by Kelpolo were actually the side or fragments of a city-Venice. In this way, the once continuous and harmonious urban space was replaced by the texture of the concept city with "one by one" personality, the distinctive personality and levelness of the city were completely subverted by the concealment and vertical characteristics of the city, and the fictional and originally related urban framework was reconstructed. In other words, we can only see the concept cities one by one, but we can never see the target cities. Borges said: "The best place to hide a leaf is the Woods." The object city is hidden in the details of each city. These secret details of the city are like a glimmer of light in the dense forest fog, and a perfect city is pieced together bit by bit by using the "residual mixed fragments, intermittent moments, and I don't know who is the receiver's signal" in memory. As long as it is stimulated enough, even for a moment, the memory can be recalled from the novel.