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Zonal Statistics
Release 9.2 Last modified January 3, 2008	Print all topics in : "Zonal (Spatial Analyst)"

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Calculates statistics on values of a raster within the zones of another dataset.

Learn more about how Zonal Statistics works

Usage tips

Command line and Scripting

Zones are defined as areas that have identical values. If the zone input is a raster, it must be integer. If the zone input is a feature class, the zone field must be integer. A character field is also acceptable.
When the zone and value inputs are both rasters of the same resolution, they will be used directly.

If the resolutions are different, an internal resampling is applied to make them match before the zonal operation is performed.

Should there be any NoData cells in the inputs, the resampling may cause there to be larger areas of NoData in your output than you might have expected. To avoid this situation, either Resample the coarser input rasters to the resolution of the finer input raster, or set the Cell Size of the Raster Analysis Environment to Minimum Of Inputs.
If the zone input is a raster dataset, it must have an attribute table. The attribute table is usually created automatically for integer rasters, but may not be under certain circumstances. You can use Build Raster Attribute Table (BuildRAT) to create one.
If the zone input is feature dataset, a vector-to-raster conversion will be internally applied to it.

To ensure that the results of the conversion will align properly with the value raster, it is recommended that you check that the extent and snap raster are set appropriately in the environment settings and the raster settings.

Since the internal raster must have an attribute table, an error will occur if one was not created in the conversion. If this happens, convert your feature dataset directly with Feature To Raster or Polygon To Raster (Point To Raster and Polyline To Raster also), generate an attribute table for it as described in the previous tip, and use the resulting raster as your Zone input.
If the zone input is a point feature dataset, it is possible to have more than one point contained within any particular cell of the value input raster. For such cells, the zone value is determined by the point with the highest feature ID.
If the zone feature input has overlapping polygons, the zonal analysis will not be performed for each individual polygon. Since the feature input is converted to a raster, each location can only have one value.

An alternative method is to process the zonal statistics iteratively for each of the polygon zones and collate the results.
It is recommended to only use rasters as the zone input, as it offers you greater control over the vector-to-raster conversion. This will help ensure you consistently get the expected results.
The input value raster can be either integer or floating point. However, when it is floating-point type, the zonal calculations for majority, median, minority, and variety will not be computed.
For majority and minority calculations, when there is a tie the output for all cell locations in the zone is assigned the lowest of the tied values.
The data type of the output is dependent on the zonal calculation being performed and the input value raster type. See how Zonal Statistics works for more information.
The following environment settings affect this tool:
- General: Current Workspace, Scratch Workspace, Output Coordinate system, Output Extent (and Snap Raster).
- Raster Analysis: Cell size, Mask.
- Raster Storage: See the Raster Storage settings for the particular output raster format selected.

ArcObjects

Zones are defined as areas that have identical values. If the zoneDataset input is a raster, it must be integer. If the zoneDataset input is a feature class, the zone field must be integer. A character field is also acceptable.
When the zone and value inputs are both rasters of the same resolution, they will be used directly.If the resolutions are different, an internal resampling is applied to make them match before the zonal operation is performed.Should there be any NoData cells in the inputs, the resampling may cause there to be larger areas of NoData in your output than you might have expected. To avoid this situation, either Resample the coarser input rasters to the resolution of the finer input raster, or set the Cell Size of the Analysis Environment to Minimum Of Inputs.
If the zoneDataset input is a raster, it must have an attribute table. The attribute table is usually created automatically for integer rasters, but may not be under certain circumstances. You can use BuildAttributeTable in IRasterDatasetEdit2 to create one.
If the zone input is feature dataset, internally a vector-to-raster conversion will be applied to it. To ensure that the results of the conversion will align properly with the value raster, it is recommended to ensure that the extent and snap raster are set appropriately.Since the internal raster must have an attribute table, an error will occur if one was not created in the conversion. If this happens, convert your feature dataset directly, and create an attribute table as described in the previous tip.
If the zone input is a point feature dataset, it is possible to have more than one point contained within any particular cell of the value input raster. For such cells, the zone value is determined by the point with the highest feature ID.
The valueDataset can be either integer or floating-point. However, when it is of floating-point type, the zonal calculations for majority, median, minority, and variety will not be computed.
For majority and minority calculations, when there is a tie the output for all cell locations in the zone is assigned the lowest of the tied values.
The data type for each value under the items in the output table is dependent on the zonal calculation being performed. See how Zonal Statistics works for the specific behavior of any statistic.
The output from the ArcObjects method is a raster object.

Command line syntax
An overview of the Command Line window
ZonalStatistics_sa <in_zone_data> <zone_field> <in_value_raster> <out_raster> {MEAN | MAJORITY | MAXIMUM | MEDIAN | MINIMUM | MINORITY | RANGE | STD | SUM | VARIETY} {DATA | NODATA}

Parameter	Explanation	Data Type
<in_zone_data>	Dataset that defines the zones. It can be a raster or feature dataset.	Composite Geodataset
<zone_field>	Field that holds the values that define each zone.	Field
<in_value_raster>	Raster that contains the values on which to calculate a statistic.	Composite Geodataset
<out_raster>	The raster to be created.	Raster Dataset
{MEAN \| MAJORITY \| MAXIMUM \| MEDIAN \| MINIMUM \| MINORITY \| RANGE \| STD \| SUM \| VARIETY}	Statistic type to be calculated. MEAN — Calculates the average of all cells in the input in_value_raster that belong to the same zone as the output cell. MAJORITY — Determines the value that occurs most often of all cells in the input in_value_raster that belong to the same zone as the output cell. MAXIMUM — Determines the largest value of all cells in the input in_value_raster that belong to the same zone as the output cell. MEDIAN — Determines the median value of all cells in the input in_value_raster that belong to the same zone as the output cell. MINIMUM — Determines the smallest value of all cells in the input in_value_raster that belong to the same zone as the output cell. MINORITY — Determines the value that occurs least often of all cells in the input in_value_raster that belong to the same zone as the output cell. RANGE — Calculates the difference between the largest and smallest value of all cells in the input in_value_raster that belong to the same zone as the output cell. STD — Calculates the standard deviation of all cells in the input in_value_raster that belong to the same zone as the output cell. SUM — Calculates the total value of all cells in the input in_value_raster that belong to the same zone as the output cell. VARIETY — Calculates the number of unique values for all cells in the input in_value_raster that belong to the same zone as the output cell.	String
{DATA \| NODATA}	Denotes whether NoData values on the Value input will influence the results of the zone that they fall within. DATA — Within any particular zone, only cells that have a value in the input Value raster will be used in determining the output value for that zone. NoData cells in the Value raster will be ignored in the statistic calculation. NODATA — Within any particular zone, if any NoData cells exist in the Value raster it is deemed that there is insufficient information to perform statistical calculations for all the cells in that zone. Therefore, the entire zone will receive the NoData value on the output raster.	Boolean

Data types for geoprocessing tool parameters

Command line example

ZonalStatistics_sa c:/data/ras_1 Value c:/data/ras_2 c:/data/final_1 MEAN DATA

Scripting syntax
About getting started with writing geoprocessing scripts
ZonalStatistics_sa (in_zone_data, zone_field, in_value_raster, out_raster, statistics_type, ignore_nodata)

Parameter	Explanation	Data Type
in_zone_data (Required)	Dataset that defines the zones. It can be a raster or feature dataset.	Composite Geodataset
zone_field (Required)	Field that holds the values that define each zone.	Field
in_value_raster (Required)	Raster that contains the values on which to calculate a statistic.	Composite Geodataset
out_raster (Required)	The raster to be created.	Raster Dataset
statistics_type (Optional)	Statistic type to be calculated. MEAN — Calculates the average of all cells in the input in_value_raster that belong to the same zone as the output cell. MAJORITY — Determines the value that occurs most often of all cells in the input in_value_raster that belong to the same zone as the output cell. MAXIMUM — Determines the largest value of all cells in the input in_value_raster that belong to the same zone as the output cell. MEDIAN — Determines the median value of all cells in the input in_value_raster that belong to the same zone as the output cell. MINIMUM — Determines the smallest value of all cells in the input in_value_raster that belong to the same zone as the output cell. MINORITY — Determines the value that occurs least often of all cells in the input in_value_raster that belong to the same zone as the output cell. RANGE — Calculates the difference between the largest and smallest value of all cells in the input in_value_raster that belong to the same zone as the output cell. STD — Calculates the standard deviation of all cells in the input in_value_raster that belong to the same zone as the output cell. SUM — Calculates the total value of all cells in the input in_value_raster that belong to the same zone as the output cell. VARIETY — Calculates the number of unique values for all cells in the input in_value_raster that belong to the same zone as the output cell.	String
ignore_nodata (Optional)	Denotes whether NoData values on the Value input will influence the results of the zone that they fall within. DATA — Within any particular zone, only cells that have a value in the input Value raster will be used in determining the output value for that zone. NoData cells in the Value raster will be ignored in the statistic calculation. NODATA — Within any particular zone, if any NoData cells exist in the Value raster it is deemed that there is insufficient information to perform statistical calculations for all the cells in that zone. Therefore, the entire zone will receive the NoData value on the output raster.	Boolean

Data types for geoprocessing tool parameters

Script example

# ZonalStatistics.py
# Description: Calculates statistics on values of a raster 
#   within the zones of another dataset.
# Requirements: None
# Author: ESRI
# Date: Sept 6, 2005
# Import system modules
import arcgisscripting

# Create the Geoprocessor object
gp = arcgisscripting.create()

try:
    # Set the input files
    inRaster1 = "c:/data/ras_1"
    inRaster2 = "c:/data/ras_2"

    # Set the output raster name
    outRaster = "c:/data/final_1"

    # Check out Spatial Analyst extension license
    gp.CheckOutExtension("Spatial")

    # Process: Zonal Statistics
    cellSize = 1
    statisticType = "MEAN"

    gp.ZonalStatistics_sa(inRaster1, "Value", inRaster2, outRaster, statisticType, "DATA")

except:
    # If an error occurred while running a tool, then print the messages
    print gp.GetMessages()

Map Algebra syntax
See ZonalMajority , ZonalMax, ZonalMean, ZonalMedian, ZonalMin, ZonalMinority, ZonalRange, ZonalStd, ZonalSum, or ZonalVariety, depending on the desired zonal statistic. For a summary of zonal statistics, see ZonalStats.

ArcObjects syntax
IZonalOp::ZonalStatistics (zone As IGeoDataset, value As IGeoDataset, type As esriGeoAnalysisStatisticsEnum, ignoreNoData As Boolean) As IGeoDataset

Parameter	Explanation
zone	An input Raster, RasterDataset, RasterBand, RasterDescriptor, FeatureClass, or FeatureClassDescriptor that identifies the zone for each value cell location.
value	An input integer or floating-point Raster, RasterDataset, RasterBand, or RasterDescriptor defining the values of the cells to be used in the zonal calculations.
type	An esriGeoAnalysisStatisticsEnum defining the zonal statistic to calculate within each zone. The enumeration types are: esriGeoAnalysisStatsMajority — Majority value esriGeoAnalysisStatsMaximum — Maximum value esriGeoAnalysisStatsMean — Mean value esriGeoAnalysisStatsMedian — Median value esriGeoAnalysisStatsMinimum — Minimum value esriGeoAnalysisStatsMinority — Minority value esriGeoAnalysisStatsRange — Range of values esriGeoAnalysisStatsStd — Standard deviation of values esriGeoAnalysisStatsSum — Sum of the values esriGeoAnalysisStatsVariety — Variety of the values
ignoreNoData	A Boolean defining the manner in which NoData values on the valueDataset that fall within a zone defined by the zoneDataset will influence the output results. If True, and if a NoData value exists in a cell on the value raster within any particular zone defined by zoneDataset, the cell will be ignored, and only cells on the value raster that have data values within the zone will be used in the processing for the output. If False, and if a NoData value exists on the value raster within any particular zone defined by zoneDataset, there is insufficient information to complete the computation of the values for all the cells within the zone, and the entire zone will receive the NoData value on the output raster and will not appear in the output table.

ArcObjects example

' Create the RasterZonalOp object
Dim pZonalOp As IZonalOp
Set pZonalOp = New RasterZonalOp

' Declare the input zone raster object
Dim pZoneRaster As IGeoDataset

' Calls function to open a raster dataset from disk
Set pZoneRaster = OpenRasterDataset ("D:\SpatialData", "zoneraster")

' Declare the input value raster object
Dim pValueRaster As IGeoDataset

' Calls function to open a raster dataset from disk
Set pValueRaster = OpenRasterDataset("D:\SpatialData", "valueraster")	

' Declare the output raster object
Dim pOutputRaster As IGeoDataset

' Calls the method
Set pOutputRaster = pZonalOp.ZonalStatistics (pZoneRaster, pValueRaster, _
                     esriGeoAnalysisZonalStatsMean, True)