Modern PKM tools such as Obsidian, Roam, and Logseq treat each note as a card-index entry: a unique address, one idea, an explicit title, and outbound links—an approach in the spirit of the wiki, with pages of internal links intended to be revised over time as understanding grows. The defining feature is the bidirectional link—recognized by both source and target—allowing navigation from either side. A graph view visualizes notes as nodes and links as edges, making it easy to spot clusters, orphans, and bridges between ideas. Daily notes are timestamped, one-per-day entries that act as both a lightweight journal and a capture inbox. Together, these patterns form what is loosely called a personal knowledge graph—the map of what concepts exist in your thinking and how they connect. Orphan notes, which have no inbound or outbound links, are usually hard to find in context and rarely reactivated; the cleanest remedies are either to edit them into the active graph or to archive them honestly.
As that graph grows, you need a way to navigate it without browsing the entire web. That is the role of a Map of Content (MOC), sometimes called a hub note: a note (not a folder) that curates and orders related atomic notes around a topic, often with commentary and cross-references. A MOC is created when a topic has accumulated several atomic notes that benefit from being introduced, ordered, and linked for future readers, including your future self. The difference between a MOC and a folder is that a folder groups files by location, while a MOC is itself a note that describes relationships. MOCs also benefit from review: a monthly MOC review adds new links, fixes broken ones, and merges topics that have grown together; tag gardening does the same for tags, pruning, merging, and renaming so the tag set stays small and meaningful rather than sprawling. The atomic principle shows up as the "one idea per note" rule in practice—if you removed any one paragraph and the rest still held a single coherent point, the note passes; otherwise it should be split.
Three more conventions increase the network's value. First, distinguish a structure note (whose job is to organize other notes around a theme) from a claim note (which takes a position or makes an argument). Descriptive notes can be wrong without misleading you, but argumentative notes carry commitments you can later test, refine, or refute. Second, prefer questions over topics when starting notes: a topic is a noun, while a question demands a position, and question-driven notes age better; the describe-and-name heuristic says that if you cannot describe an idea in one sentence and give it a clean title, you do not yet understand it well enough to save it as a permanent note. Third, prefer context tags ("@meeting," "@errand") or value-based tags ("#principle," "#example," "#counterexample," "#question") over sprawling topic tags, because role-based tags carry information that titles often cannot. Search usually beats folders, since it matches on content rather than on a single filing decision; beware the "first in, last out" trap where the newest notes get the most attention while older, possibly more valuable ideas go unread for years. A trusted index file—a small set of notes listing your main MOCs, areas, and projects—gives you a place to start the day.