When should I use a single-select field, a multi-select field, or linked records?

For your case, the first question is whether a city is just a label or something your team needs to manage as its own record.

• Single-select fits a field that has exactly one value. Since one service area may cover several cities, it does not fit your current “cities covered” field.
• Multi-select is the simplest choice if you only need to tag each service area with city names. It works well while the list is small and you do not need city-specific fields or a shared city record.
• Linked records are the better starting point if cities will have their own coordinator, region, service description, or other details that several service areas should reuse. Make a Cities Base (city name plus a stable identifier or region to distinguish names), then link each Service Area record to the relevant city records. This gives the city one place to update instead of copying its details into every area.

One extra distinction matters: if the coordinator or services are different for the *same city in different service areas*, they belong to that area–city assignment, not to the city itself. In that case, use a third Coverage Base with one record per service-area/city pair, linked to both, and fields for its coordinator and service details.

Because you already expect more city data later, I would start with linked records. You can see the available field types and how Bases organize those records. Where would the coordinator belong in your process: to the city overall, or to each service-area/city assignment?