Supply chain tier mapping extends visibility beyond direct (Tier 1) suppliers to include their suppliers (Tier 2), sub-suppliers (Tier 3), and deeper tiers where critical materials, components, or services originate. This comprehensive mapping reveals hidden concentrations, geopolitical exposures, and cascading failure points invisible in single-tier analysis. The 2011 Japan earthquake demonstrated tier mapping's importance when automotive manufacturers discovered critical component dependencies three or four tiers deep. Mapping requires supplier collaboration, technology platforms, and continuous updates as supply networks evolve. Deep-tier visibility enables proactive risk identification, alternative sourcing strategies, and resilience planning for critical inputs.