Direct answer
A migration map connects each valuable old URL to the closest real new equivalent; removed content should return an honest status when no equivalent exists.
Practical steps
- Freeze and normalize inventories.
- Classify unchanged, moved, merged and removed intents.
- Create direct one-hop permanent mappings.
- Test before launch and monitor after.
Common mistakes
- Redirecting everything home.
- Building chains.
- Changing platform, content and measurement without baselines.
Limitations
- Not every signal transfers predictably.
- Large inventories require sampling and monitoring.
Primary sources
- Understand the JavaScript SEO basics — Google Search Central; 2026-03-04; 2026-08-14.
- A Quantitative Study of Forum Spamming Using Context-based Analysis — NDSS Symposium; 2007-02-28; 2026-08-14.