Do you need a separate landing page for every city you serve?

No. You need a city page only when it passes three tests: real search demand, real service coverage, and enough unique substance to justify existing. Fail any one of them and the page is a liability rather than an asset.

The three part test

• Demand. Do people actually search your service plus that city? Check a keyword tool, your Search Console queries, and your paid search term report. Many suburbs have no meaningful volume for your service, and a page cannot create demand that is not there.
• Coverage. Do you genuinely serve that city, regularly, and would you take a job there tomorrow? If not, the page will attract leads you decline, which wastes your time and theirs.
• Substance. Can you write 500 words about your work in that city that could not be copied onto another city's page by swapping one word? If not, you do not have a page. You have a template.

What a city page needs to contain

Named projects or jobs completed there. Photos from that area. Reviews from customers in that city. Specifics that are locally true: the neighborhoods you work, the permit office you deal with, the response time from your base, the seasonal problems particular to that area. Your NAP and a clear call to action. A map is fine. A map plus 200 generic words is not a page.

Why thin city pages hurt

Publishing 40 near identical pages tells Google you produce low value content at scale. It dilutes internal linking across pages that will never rank, and it gives a prospect who lands on one a page that says nothing. Ten real pages beat forty templates, and the ten are cheaper to maintain.

The honest version most agencies will not give you: if a city page cannot pass the substance test, skip it. Strengthen your Google Business Profile and buy paid search in that city instead.

Related: How do you do local keyword research?, Multi-location local SEO, Do you handle website copywriting?, website design and UX.