Lookup (Spatial Analyst)

Summary

Creates a new raster by looking up values found in another field in the table of the input raster.

Illustration

OutRas = Lookup(InRas1, "Category")

Usage

• Lookup supports fields that are numeric (integer or floating point) or string. If the field is integer or string, the output will be an integer raster; otherwise, the output raster will be a floating-point raster.

• If the lookup field is of integer type, the values of that field will be written to the output raster attribute table as Value. Other items in the input raster attribute table will not be transferred to the output raster attribute table.

  For example, an attribute table of input raster with numeric field Attr1:

      Value   Count   Attr1
      1       294     1
      2       345     8
      3       654     3

  Output attribute table from Lookup on Attr1 field:

      Value   Count
      1       294
      3       654
      8       345

• If the lookup field is a string type, the lookup field will appear in the output raster attribute table, and the value field will be the same as for input raster. Any other items in the input raster's attribute table will not be transferred to the output raster's attribute table.

  For example, consider the attribute table of an input raster with string field Text1:

      Value   Count   Attr1   Text1
      1        294    1       A
      2       6218    8       B
      3         28    3
      4       3603    9       3

  The attribute table of the output raster from running Lookup on the Text1 field would be:

      Value   Count   Text1
      1        294    A
      2       6218    B
      3         28    
      4       3603    3

Syntax

Lookup (in_raster, lookup_field)

Parameter	Explanation	Data Type
in_raster	The input raster that contains a field from which to create a new raster.	Raster Layer
lookup_field	Field containing the desired values for the new raster. It can be a numeric or string type.	Field

Return Value

Name	Explanation	Data Type
out_raster	The output raster whose values are determined by the specified field of the input raster.	Raster

Code Sample

Lookup example 1 (Python window)

This example creates a new raster determined by the specified field of the input raster.

import arcpy
from arcpy import env  
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"
outRaster = Lookup("mycity","land_code")
outRaster.save("C:/sapyexamples/output/mylandcode.img")

Lookup example 2 (stand-alone script)

This example creates a new raster determined by the specified field of the input raster.

# Name: lookup_example02.py
# Description: Creates a new raster by looking up values found in another 
#              field in the table of the input raster.
# Requirements: Spatial Analyst Extension

# Import system modules
import arcpy
from arcpy import env
from arcpy.sa import *

# Set environment settings
env.workspace = "C:/sapyexamples/data"

# Set local variables
inRaster = "mycity"
lookupField = "land_code"

# Check out the ArcGIS Spatial Analyst extension license
arcpy.CheckOutExtension("Spatial")

# Execute Lookup
outRaster = Lookup(inRaster, lookupField)

# Save the output 
outRaster.save("C:/sapyexamples/output/mylandcode")

Environments

Cell Size, Current Workspace, Mask, Output Coordinate System, Extent, Scratch Workspace, Snap Raster

Licensing Information

ArcGIS for Desktop Basic: Requires Spatial Analyst or 3D Analyst

ArcGIS for Desktop Standard: Requires Spatial Analyst or 3D Analyst

ArcGIS for Desktop Advanced: Requires Spatial Analyst or 3D Analyst