IN WHICH you move into an entirely different realm of GIS analysis and geoprocessing: solving problems with a method of data representation—called raster, grid, or cell-based—that is dramatically different from what you are used to.
Raster is faster but vector is corrector. Berry, JK, 1995
You have briefly met rasters before in this book. Most images are stored in raster format. The COLE_DEM of Chapter 1 stored elevations in floating-point raster format. And you saw rasters that stored landcover in integer raster format. What is new here is that you will do GIS analysis using raster representation.
To be candid, it would take another book the size of this one to cover the immense subject of raster processing. Up until a few years ago, it was almost completely divorced from GIS vector processing. Esri has done a good job in taking down the barriers between the two. In terms of GIS data model development, raster processing (or grid processing, or cell processing, which are other terms for it) preceded vector processing. It was, at one time, about the only way to get large amounts of geographic data into the memories of the then-small computers. (100 Kilobytes of storage was a lot in 1960.) In the following years vector processing, with its greater capacity for precision, tended to supersede raster processing in terms of popularity for solving GIS problems. It is now understood that raster processing has some properties that make it ...