Definition

URL mapping table for a site migration

A URL mapping table is the complete list that matches every address on the old site to its address on the new one, before a redesign or a platform change. It covers pages, downloadable files and embedded content. It is used to write the redirects: a complete table can make the migration a non-event, while a partial table loses traffic.

What a URL mapping table contains

Each row matches an old address to its destination. A working table often adds the redirect type (a 301 sends the old address to the new one automatically and permanently), the traffic and links the old page received, and a verification column filled in after launch.

The table is not limited to important pages. It includes every address that exists, including the ones nobody visits anymore but that still receive links from other sites.

Where the addresses come from

Three sources combine: a full crawl of the old site (what exists), the addresses known to search engines (what they have indexed), and the pages that received traffic or links over the last twenty-four months (what actually matters).

A standard crawl also misses embedded files (images, videos, scripts), downloadable documents and ad pages outside the navigation.

The two most costly mistakes

The first is redirecting every page without an equivalent to the home page. Google warns that mass redirects to the home page can be treated as not-found pages. The right destination is the closest page by topic; if none exists, the page can simply disappear.

The second is stacking a new rule on top of old redirects. A site that has already migrated once then creates redirect chains. Google recommends pointing each old address directly to its final destination.

Example

Fictional example: a renovation company replaces its website. Here are four rows from its table.

  • The address /services/roofing.html redirects with a 301 to /roofing/: the topic is the same.
  • The document /docs/roofing-warranty.pdf redirects with a 301 to /documents/roofing-warranty.pdf: it still receives links from a trade association.
  • The ad page /spring-promo/ redirects with a 301 to /quote/: its address still appears on printed posters.
  • The page /blog/news-2016/ has no traffic, no links and no equivalent: it disappears, with no redirect to the home page.
How we read it

We treat the URL mapping table as the one migration deliverable that decides the outcome. Google states that 301 redirects cause no loss of PageRank (the importance score it gives each page): what loses traffic is forgotten addresses. A serious proposal therefore sizes the table in number of addresses, documents and embedded content included.

We also record traffic, inquiries and organic revenue before the switch. Without that record, nobody can prove afterwards that the migration worked.

Not to be confused with

301 redirect
A 301 redirect is the technical rule that sends an old address to the new one. The URL mapping table is the plan that says which redirect to write for each address.
XML sitemap
A sitemap lists the current addresses for search engines. It helps Google discover the new addresses, but it says nothing about the old ones.

Related concepts

Further reading

Related services

Frequently asked questions

Who should prepare the URL mapping table?

The provider building the new site prepares it. Require it in the quote, sized in number of addresses, documents and embedded content included.

How long should redirects stay in place?

Google recommends keeping them as long as possible, generally at least a year.

My traffic dropped after the migration: did it fail?

Not necessarily. Google indicates that rankings can fluctuate for a few weeks while it recrawls the site. Watch the not-found errors: they reveal what the table missed.

← The full glossary