Each pair of cities is connected by a direct road.

We're in talks with a couple of cities to that end.

We’re in talks with a couple of cities to that end.

Paul — a pair of Minnesota cities, the most commonly known Twin Cities

You are talking about a market; the market is defined as a city pair.

Exchanges are only permitted for the same city pair or route originally booked.

I defined weights for each pair of cities as a function of the Euclidean distance between them and the number of friends between them.

I defined weights for each pair of cities as a function of the Euclidean distance between them and the number of friends between them.

The route Paris – Geneva is the city pair linking the country with another European destination, that was the most popular in 2017.

I defined weights for each pair of cities as a function of the Euclidean distance between them and the number of friends between them.

I defined weights for each pair of cities as a function of the Euclidean distance between them and the number of friends between them.