What Is Redirect Mapping?
Redirect mapping is the document that pairs every old URL on a site with the one new URL it should send visitors and crawlers to during a migration.
Redirect mapping is the document that pairs every old URL on a site with the one new URL it should send visitors and crawlers to during a migration. It is not the redirect rules themselves. The map is the decision record, written by whoever knows the content; the rules are the implementation, usually written by someone else.
Why the map is the migration
Every link anyone has ever pointed at your site points at an old URL. So does every bookmark, every citation, and every ranking position you currently hold. A migration does not move those things. It abandons them unless a redirect carries each one to a specific replacement.
The damage from a bad map is delayed, which is what makes it dangerous. Launch week looks fine because the new site works. Weeks later, rankings on pages nobody thought to check have gone, and the cause is buried in a spreadsheet decision made under deadline pressure. Recovery costs more than the mapping would have, which is worth weighing against what a safe migration costs when the quotes come in and the cheapest one has no mapping line item.
How a redirect map is built
- Gather URLs from several sources, not one. A crawl of the live site finds what is linked internally. It misses orphans, old campaign pages, and URLs that only external sites and old emails still reference. Those come from other exports.
- Deduplicate and normalise. Strip session parameters, unify trailing slashes, and collapse case variants. You want one row per genuine destination, not four rows describing the same page.
- Match one old URL to one new URL. The replacement should serve the same intent. Close is fine, related is not, and a category page is a reasonable fallback only when it genuinely covers the topic the old page covered.
- Rank the rows by value. Sort by external links, then by sessions, then by impressions. If time runs out, the top of that list is where accuracy actually matters and the tail can take a sensible pattern rule.
- Choose the status code deliberately. Permanent moves need the permanent code, so consolidation signals pass as intended, which is why it pays to know exactly which status code signals permanence before the rules get written.
- Mark deliberate deletions. Some pages should not be redirected anywhere. A retired page with no equivalent and no links can return a proper gone or not-found response. That is a valid decision, recorded in the map, not an omission.
- Test the map before launch, then verify after. Run every source URL on staging and check the response code and the final destination. Re-run the same list the day you go live, because rewrite rules behave differently in production.
| URL source | What only this source catches |
|---|---|
| Crawl of the live site | Everything currently linked from your own navigation |
| XML sitemaps, including archived ones | Pages you published and quietly unlinked |
| Search Console performance export | URLs earning impressions that nobody internally remembers |
| Backlink export | Old URLs other sites still point at, including ones already deleted |
| Server logs | What crawlers and users still request, including URLs missing everywhere else |
The blunt version
Redirecting everything to the homepage is treated as a soft 404. It is the single most common migration failure, and it is not a shortcut that costs you a little. Google documents this behaviour plainly: a redirect to a page that does not serve the original content gets classified as a soft 404, and a soft 404 passes nothing. The old URL drops out. The link equity does not arrive anywhere.
It keeps happening because it looks like success on the dashboard. Point every unmatched URL at the homepage and your 404 report goes clean overnight. Somebody reports that the migration went smoothly. The traffic loss shows up a month later, attributed to an algorithm update rather than the rule that caused it.
The honest rule is simpler than the workaround. If a relevant replacement exists, map to it. If it does not, return a proper not-found or gone response and accept the loss on that URL. A truthful 404 costs you one page. A blanket homepage redirect costs you the accumulated authority of every page you swept into it, and this is the failure that quietly follows most teams through a platform switch.
Example
Say a retailer replatforms and 3,000 of its 12,000 URLs have no direct equivalent, mostly discontinued products. The build team maps the 9,000 matches correctly and sends the remaining 3,000 to the homepage to clear the error report before launch. Six weeks later, category rankings have slipped and referring domains that pointed at those discontinued products are passing nothing. The repair is unglamorous: re-map each discontinued product to its parent category where one exists, return a gone response where none does, and reinstate internal links to the surviving pages. The map should have said that in the first place, and none of the repair work is difficult. It is simply being paid for twice.
FAQ
Can I redirect a page to the homepage if nothing else fits?
Not usefully. Google treats a redirect to a page that does not cover the original content as a soft 404, so nothing transfers. A relevant category or parent page is a legitimate destination. When neither exists, returning a not-found or gone response is the honest and safer answer.
How long should migration redirects stay in place?
Google advises keeping them for at least a year, and there is rarely a good reason to remove them after that. External links and bookmarks outlive your patience. Removing redirects later reintroduces the same losses you spent the migration avoiding, usually without anyone connecting the two events.
Do I need to map URLs that get no traffic?
Check their links before deciding. A page with no sessions can still hold external links worth keeping, and traffic reports will not show you that. Pull a backlink export alongside your analytics, then map anything with references pointing at it and let genuinely dead URLs return a proper error.
Related terms
- 301 Redirect — the permanent status code your map’s decisions get implemented as.
- Redirect Chain — what an unmaintained map turns into after the second migration.
- Manual Action — a separate, human-issued problem that redirects cannot repair or escape.
A clean 404 report is not evidence of a clean migration; it is often evidence that someone swept the difficult rows into the homepage. Ask to see the map, not the error count.