When you learn to slow down your reading you will be able to see that all writing is made up of parts and layers that come together in the writing process to make something that seems whole. For example, here are three maps of the United States. The first is a traditional overview map of the United States. Consequently, the United States and Western Europe appear larger than they really are. This is a poem about a map of the United States.
Maps have one purpose and murals something else, just as maps are one thing, and poems are another.
Yet, when you consider the three maps side by side, you can see that even maps are a matter of perspective, that even maps tell a story of the context from which they are drawn. Similarly, Rich seems to be implying that maps and murals are not that different because places and their stories are hard to separate, just as no form of representation can be separated from the perspective that produces or sees it. Another way to think of this is that the maps and the poem are all representations of the United States. None of the texts, the maps or the poem, is the United States itself but a symbolic version of it. In other words, texts are not the things they talk about, but representations of the things they talk about.