Geographic addressing (GA) is a way of addressing messages in a network. In GA, the destination of a message is specified as a geographic region. The network delivers the message to all devices in that region. A representative application is to distribute Common Operating Picture updates to interested devices. This paper extends previous research on GA to handle challenging problems arising in real-world implementations: large scale, network heterogeneity and multiple security domains. After first laying out the problem and challenges, we describe SGAF, a scalable geographic addressing framework for building and combining scalable GA systems. We illustrate and evaluate SGAF using a case study of one implementation of the framework, the AT&T Labs Geocast System.