A polygon layer and at least one raster layer must be loaded into ArcMap in order to use this
tool. The polygon layer must contain an attribute field (other than the FID) that
represents a unique ID number (an integer) for each polygon. This field is used in the
naming of the clipped rasters so that a raster clip can be easily tied back to the
original polygon. THE POLYGON LAYER AND RASTER LAYERS MUST SHARE THE SAME PROJECTION.
If they do not, you will have to reproject the layers so that they do share the same
projection or you will get nonsensical results or no results at all.
Naming convention for new rasters.
Within the output folder you specify a new folder is created that has the same name
as each of the rasters that you elected to clip. Within each of these folders, a
new raster layer is created with the following naming convention: r + unique_id, e.g.
r149 corresponds to the raster clip for the polygon with the unique ID 149.
Why not all polygons result in a clip.
If a polygon does not overlap the raster layer at all, it is simply ignored (partial
overlaps are processed). If a clipped raster already exists with the unique ID that
is currently being processed (i.e. if the unique ID's are not actually unique and
duplicates occur) then the polygon is ignored.
Raster layers in ArcMap display a maximum of 3 bands. A raster dataset on a disk
can have more than 3 bands. This tool accesses the raster dataset on the disk
to ensure that all the bands in the raster are retained in the new raster layer,
not just the three bands that are loaded in ArcMap. The order of the bands is also
retained in the new raster layer.
Why the new rasters may not look like the old raster.
Raster band statistics are recalculated for the new clipped rasters. For all rasters
and particularly for images (e.g. orthophotos) this can affect the way they look
in ArcMap because these statistics are used to create a colour scheme for the new
raster. The cell values of the rasters do not change - only the way they are displayed.
If you get an uninformative error message when trying to use the tool.
This tool requires access to a Spatial Analyst license. The very first thing to check
if you get an error message is that you have a license available (look under Extensions
to ensure that the Spatial Analyst license box is checked).