A redesigned website loses its search rankings when the addresses that earned them change or disappear without a plan, not because the new design looks different. Search engines rank addresses, and every address that used to receive visitors and links has to either survive or point, permanently, to its closest equivalent. A redirect map is therefore the part of a redesign that decides the search outcome, and the part least often seen in a quote.
That also gives you a way to judge a proposal. Ask to see the redirect plan before the designs. A studio that has one has thought about your existing audience. One that does not is planning to meet it again from scratch.
Inventory comes before design
Before anything is drawn, list every address on the current site that matters: the ones that receive visits, the ones other sites link to, the ones that appear in search results. The sources are your analytics, your search console data and the old sitemap, and none of them is complete alone. A page nobody navigates to can still carry the one link a major publication gave you.
This list is the real brief. A design that cannot accommodate the pages on it is a design for a different site.
Decide the fate of each address
Every address on the list gets one of three outcomes: it stays exactly as it is, it moves to a new address that is permanently redirected from the old one, or it is retired because nothing replaces it. The cheapest outcome is the first. If the old address is sensible, keep it, even if the page behind it has been completely rewritten; there is no rule that says a new design needs new addresses.
Where an address must change, the redirect should point to the page that now answers the same question, not to the nearest convenient page. A redirect is a statement that this is the same thing, moved, and a search engine will test it against the content it finds.
Why sending everything to the homepage fails
The tempting shortcut is one rule that sends every old address to the home page. It satisfies a checklist and discards the work: a visitor looking for a specific service lands on a general page that does not answer them, and a search engine that follows the redirect finds that the destination does not match the content it used to rank. Treated as irrelevant, the old address stops passing on what it had earned.
Redirects also should not chain. If an old address goes to an intermediate address that itself redirects, every hop adds delay and risk. Point each old address directly at its final destination.
The content has to survive too
A page ranks because of what it says, and a redesign is the moment that text is most likely to be cut for the sake of a cleaner layout. If the paragraph that answered a question people search for disappears, a perfect redirect leads to a page that no longer deserves the position. Before cutting copy, check what each page was found for, and keep the part that earned it.
Measure the old site before you touch it
Record where the site stands while the old version is still live: the pages that bring visitors, how many addresses are in the index, the positions that matter, and the number of enquiries. After launch these figures are the only way to tell a normal adjustment from a real loss, and they cannot be reconstructed once the old site is gone.
Keep the new site out of search results while it is being built, with a password or a noindex instruction, and write down that this must be removed at launch. A staging site that goes live still blocked from indexing is a common and entirely avoidable way to lose months.
Check after launch, and expect movement
On the day the new site goes live, test the list. Request each old address and confirm that it answers with a permanent redirect to the right place, then watch the search console coverage and error reports over the following weeks for addresses you missed. Missed addresses are normal, and they are cheap to fix in the first month and expensive to discover in the sixth.
Be wary of anyone who promises that rankings will not move. Even a careful migration is followed by a period of adjustment while search engines re-read the site. What a good redirect map buys you is that the movement is temporary and small, rather than permanent and large.