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In this video I'll demonstrate how to create a new grid
based on an existing field in a LANDFIRE Existing Vegetation Type grid
attribute table. I'll be working in ArcGIS 10
but a similar process can be used in other versions of Arc.
There are a variety of reasons why you might want to create a new grid from an
existing field.
LANDFIRE vegetation grids in particular come with several levels of
classification
and you may want to create a grid based on one of the secondary attributes in the table.
You can see in the value attribute table from the Existing Vegetation Type grid
that I have open here
that there are six different existing vegetation types
but some of them are quite similar. For example,
the first two are variants of a Douglas fir hemlock forest.
You can see that these are both classified by the same system group name
and system group number. Likewise LANDFIRE mapped two similar hemlock silver
fir forest types
that are both classified by the same system group name and number.
I'm going to simplify the tapes in this grid by creating a new grid
based on the system group name field. This will reduce the number of vegetation
types in the grid from six to four.
To do that, open up the ArcToolbox
Spatial Analyst tools then select
the reclass menu and the lookup command.
Drag and drop the Existing Vegetation Type grid
into the input raster field. Then
from the lookup field dropdown select the system group name.
Check the output raster location
and click OK. At the bottom of the screen,
you will see a message that the lookup command is working and the new grid
will be added to the project table of contents when it is complete.
Opening the new value attribute table,
you can see that a unique value was assigned to each name in the system
group name field
and the number of types in the Existing Vegetation Type grid
has been effectively reduced. You may want to use the join function to rejoin
some of the original attributes back to the table
such as the system group number.