A topic cluster is a content architecture model where you organize related content around a central pillar page and supporting subtopic pages. The pillar page covers a broad subject at a high level—say, "SEO for local businesses"—while 8 to 15 cluster pages dive deep into specific aspects like "Google Business Profile optimization," "local citation building," or "schema markup for storefronts." Every cluster page links back to the pillar, and the pillar links out to each cluster page, creating a tightly connected hub. This structure replaced the old one-keyword-per-page approach because Google now understands semantic relationships between topics. When you interlink a cluster properly, you signal topical depth and authority, which tends to lift rankings across the entire group. We've seen pillar pages rank for competitive head terms while cluster pages capture long-tail variations and related questions. The pillar page typically runs 2,500 to 4,000 words and provides enough detail that someone unfamiliar with the topic walks away informed, but it doesn't exhaust every nuance. Cluster pages run 1,200 to 2,500 words each and target more specific search intent. For Ottawa SEO's portfolio, we might build a pillar on "link building strategies" and create clusters for outreach tactics, broken link building, digital PR, and HARO—each with its own keyword set and conversion path. The mistake most sites make is building clusters that overlap too much or picking subtopics with no search volume. Each cluster page should answer a distinct question and ideally target a keyword with measurable monthly searches. You also need internal links beyond the hub-and-spoke—cluster pages should link to each other when contextually relevant, not just back to the pillar. That cross-linking reinforces the topic network and keeps users engaged longer, which helps dwell time and reduces pogo-sticking. Done right, a topic cluster becomes a self-reinforcing SEO asset that compounds authority over time.