Setting the analysis environment

Most Spatial Analyst operations result in the creation of a new output raster, most often a grid. The settings you select in the Analysis Options dialog control the geometry of the output grid (cell size, extent, processing mask, and projection). You may also set the working directory, where output grids will be created by default.

Input Raster	Analysis Extent	Analysis Cell Size	Analysis Mask	Output Raster

Although all of these settings have defaults, it's a good idea to set them before performing an analysis. While the analysis environment settings are used automatically when a new raster is created, some functions allow you to override certain settings like cell size.

The cell size
You can specify the size of the output cells, which may be different than any of the input rasters.

The extent
You can set the width and height of the output raster, which may also be different than any of the input rasters. A snapping layer associated with the extent can adjust the boundary of the specified extent to match another raster or vector layer.

The mask
You can specify a processing mask (either a raster or vector layer) to identify cells that will be set to NoData in the output.

The projection
You can set the projection of the output raster to match a previously added layer, or the projection of the ArcMap data frame, which you may also set.

The working directory
You may specify the path to a directory where new output data will be created. If you don't include a path in their names, ArcGIS Spatial Analyst assumes that any input datasets referenced by their source name, as opposed to their layer names, exist in the working directory. This mostly affects specifying input data in Map Algebra expressions entered in the Raster Calculator.