All of Botticelli's drawings for Dante's Divine Comedy measure approximately 30cm by 47cm in order to fit into the final manuscript.
The theme of this chapter is the path to the Empyrean, with Dante and Beatrice in the river of light. As a result, much of the detail is devoted to the various plants that make up this garden, with then the two figures placed in the foreground in the centre of the composition.
This romantic sketch tells the story of how Dante now feels unable to put the beauty of Beatrice into words. Nature as well as the seasons proved significant in Botticelli's paintings as well with famous frescos such as Primavera and The Birth of Venus. He would create stunning detail across the background with plants swirling in a similar fashion to the detail in Tree of Life and The Kiss by Gustav Klimt.
The depiction of plants and flowers gives artists an opportunity to use stunning flourishes be it with drawing or painting. Botticelli tended to use them as content for his backgrounds and the topic of Canto XXX with its garden references gave him an ideal opportunity to go down this path.
You will again find contrasts between the underdrawing and the darker finished lines of the completed drawing, offering evidence of Botticelli again changing his mind over the precise composition of this work. Indeed, one advantage of using pen and brown ink over metalpoint on vellum is that subtle lines can be amended as an artist changes his mind. Botticelli would also sometimes amend his paintings directly when he had not taken time to complete study pieces.