1. A method comprising the steps of: (a) processing frames from a source video sequence by matching image content of said frames to image data from a geographic database to derive the geographic locations of pixels within at least part of said frames; (b) compressing said source video sequence by a lossy video compression technique to generate a compressed video sequence; and (c) encoding said compressed video sequence together with data indicative of said geographic locations of pixels as a composite data stream, wherein said data indicative of said geographic locations includes: (i) a geographically registered elevation map selected from the group consisting of: a digital terrain map and a digital model of an urban landscape, and (ii) at least four geographically anchored reference points per frame associating a pixel of said frame with a location in said geographically registered elevation map.