Output rasters

By default, most Spatial Analyst operations create output rasters in ArcInfo GRID format, which may be either temporary or permanent. Grid names have certain limits—they must have twelve or fewer characters, cannot have embedded blanks, and should only contain characters A-Z and 0-9.

Temporary grids
Unless you name an output grid, it is created with temporary status. This means that it is automatically deleted if you quit ArcMap without saving your work, or if you remove its corresponding layer from the ArcMap Table of Contents. The temporary grid will be stored in the working directory you specified as one of the analysis options and will be given a default name, like “Calc1”. A layer with a default name will be created in the Table of Contents.

You can make a temporary grid permanent by right-clicking its layer in the Table of Contents and choosing Make Permanent from the context menu that appears.

Permanent grids
Most Spatial Analyst dialogs have controls that allow you to name the output grid and to choose the directory in which it will be created. Additionally, many dialogs allow you to specify the output format—GRID, TIFF, or ERDAS Imagine. Naming an output grid makes it permanent.