1) I notice that Foursquare does not show all places, but other engines show places that are not yet in Foursquare, but I would like to use Foursquare API, so is there a problem showing a merged view of places from more than one engine providing attributions to both?
2) Even if I don't use both engines, but only foursquare and I create my own places (no other engine but my own), can I show a merged view of both of them?
If the above is not possible, what are my options of a location database that allows the above?