In July and August of this year Canada is hosting four international organization concerned with the exploration and development of the earth and man's activities on the planet. More than 15,000 delegates from some 125 countries will take part in various activities of the 22nd International Geographical Congress, the 24th International Geological Congress, the 6th International Conference of the International Cartographic Association and the 12th Congress of the International Society of Photogrammetry, the major assemblies of which are being held in Montreal and Ottawa. The presence in Canada of these four international organizations gives implicit recognition to the work of Canadians in the field of earth sciences. The release of four appropriate Canada Post Office stamps, each with a denominative value suitable for use on mail destined for a large part of the earth's surface, provides evidence of the significance attached to these events in the host country. Spectacular advances have occurred in recent years in the application of photogrammetry to topographical and cadastral surveys, to planning and engineering, and to the investigation, survey and assessment of natural resources. Moreover, the range of interest has widened to include applications to medicine and work on bodies in inner and outer space. The stamp for the 12th Congress of the International Society of Photogrammetry is a visual simplification of the theme. The white space represents the area on the ground within range of a camera lens at a high altitude. Within this area are two sun-lit mountains, simplified to two prisms. The black lines meet at a high elevation which represents the approximate position of the aircraft carrying the camera.