Sharing content within an evolving content-sharing zone

A user selects a content item that he wishes to send. He then performs a "sending" gesture and specifies an initial "content-sharing zone." In order to be eligible to receive the selected content item, a receiving device must be located within the content-sharing zone. However, the content-sharing zone can evolve over time. It can grow in size, change shape, or move (e.g., it can remain centered on the sending user as he moves). A potential recipient makes a "receiving" gesture, and, if the location of the receiving device is located within the evolving content-sharing zone, as currently defined, then the content item is sent from the sending device to the receiving device (either directly or via a content server). A maximum size or duration of the evolving content-sharing zone can be specified. Other restrictions can be stated so that, for example, only intended recipients can receive the content item.