Although the raster type is vastly different in makeup from the geometry type, in PostGIS you’ll find the two have a very fluid relationship. In this chapter we'll mostly focus on raster functions that take as input a single raster or a geometry and output a scalar value, another raster or another geometry. In chapter 9 and 12 we'll explore interaction between raster and geometry in more detail when we explore the spatial relationships supported between the two and how leveraging these relationships makes it easy to do statistics on bounded geographic regions, clip rasters with geometries, and create hybrid rasters by overlaying several rasters.
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