Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

Rasters with Floating-Point Values

Rasters with floating-point cell values are used to store what is called continuous data. Such data may also be referred to as nondiscrete data, field data, or surface data. The numbers are stored in a format that allows many significant digits and great range. A given cell may well have a different value in it than any other cell in the raster. The concept of a zone does not apply, since most of the zones would probably consist of a single cell and, therefore, usually, no value attribute table. The values in a floating-point raster usually represent magnitude, elevation, distance, or relationships of cells to other nearby cells in that or some other raster. A major use for floating-point rasters is to represent surfaces, such as elevation of the Earth’s surface, or surfaces derived from point data such as rainfall over an area. The word “continuous” is something of a misnomer. There are abrupt changes in Values at the boundaries of cells. The amount of change at boundaries can be reduced by using more and more cells—that is, higher resolution—but, at the conceptual level, the lumpiness of the surface remains. See Chapter 6 for a discussion of continuous and discrete phenomena.