In this “false color” composite image of the United States, we find a satellite’s view of the nation in 1976. Brighter reds indicate dense vegetation, while urban areas emerge in shades of gray and blue. This imagery was collected from two satellites—Landsat 1 and Landsat 2—which entered orbit in 1972 and 1975, respectively. The back of this informational poster describes resource management workflows like crop monitoring, flood control, and oil exploration as key contexts in which satellite imagery would aid the “monitoring of America’s resources from space.” However, it’s important to remember the geopolitical conditions under which this map was produced. As the quote below indicated, a robust satellite imagery program had great potential for gathering military intelligence, so it’s no accident that satellite programs and the geospatial technology to process and analyze them emerged in tandem with a push for military dominance during the Cold War.
We’ve spent $35 or $40 billion on the space program. And if nothing else had come out of it except the knowledge that we gained from space photography, it would be worth ten times what the whole program has cost. Because tonight we know how many missiles the enemy has.
Satellite imagery represents a fundamentally different answer to the question of how you encode the world as geospatial data. Unlike the vector data structure—which encodes all features as points, lines, or polygons—satellites images are composed of continuous grids containing billions of individual pixels known as rasters. Each cell in a raster’s grid corresponds to a single pixel, and each pixel corresponds with a particular unit of spatial measurement, like 10, 50, or 100 meters. If you zoom in far enough to any raster image, and you’ll start to notice the pixelation. While the “space portrait” shown here has the appearance of a unified, unbroken image, it is actually a mosaic of hundreds of smaller rasters, each measuring about 13,000 square miles and stitched together using geographic information systems (GIS) software.