It would be great if we could, for example, pass a city name and x mile radius for a list of cities that are within the x mile radius of a city.
It would certainly make a project I'm working on right now extra cool.
PlaceFinder is a geocoder, not a spatial search tool. We do have another web web service, GeoPlanet Web Service, that offers a neighbors resource (see http://developer.yahoo.com/geo/geoplanet/g...#api-neighbors) that returns a list of places that are adjacent to a given place. We think this is a better solution than using airplane distance between city centroids for determining the relationship between nearby cities. Take a look at the documentation to see if it can meet your needs.