The Sutta Pitaka is where most of what is commonly called "Buddhist scripture" in the sense of recorded teaching actually lives: thousands of individual discourses, most attributed directly to the Buddha and a smaller number to senior disciples speaking with his approval, arranged not by chronology or by subject alone but by length and structural convention into five collections, or nikayas. The Digha Nikaya gathers the longest discourses, often addressed to specific audiences on significant occasions; the Majjhima Nikaya holds middle-length discourses covering a wide range of doctrinal and practical topics; the Samyutta Nikaya groups shorter discourses by connected theme; the Anguttara Nikaya organizes material numerically, by lists of one item, two items and upward; and the Khuddaka Nikaya collects everything shorter and more varied that does not fit the other four, including verse collections, birth stories and other miscellaneous material.
This atlas already records some of that material at a finer grain than the basket itself, the individual nikayas and specific texts within them among its existing rows, so the Sutta Pitaka functions here as the organizing division that holds those finer-grained portions together, the layer between the whole Tripitaka and its individual named discourses and collections.