Raster consists of a grid of cells arranged in rows and columns. Think of raster like pixels on a screen, except each pixel is defined using a set ground distance. There is a lot in common between raster files and image files. Raster files are sometimes saved using the same formats as image files. Images are often created straight from raster files; you see such examples all the time, from weather forecasts to terrain maps.
The size of the cells in the grid is similar in concept to the resolution of an image. Unlike vector data, a raster contains information for the entire area it covers. It is useful for things that have values for an entire area, such as elevation and temperature. The downside is the resulting large file sizes.
Multiple values per cell can be stored as different bands in the dataset. This is similar in concept to RGB values for a color image. The SRTM and Digital Elevation Model (DEM) datasets discussed in Chapter 7, Decorating Your Data - Adding External...
