Arcgis Calculate Mean of Rasters Ignore 0

Calculating the mean of multiple rasters in ArcGIS while ignoring zero values is a common task in spatial analysis. This guide explains the process step-by-step, provides a built-in calculator, and includes practical examples to help you understand and apply this technique.

How to Calculate Mean of Rasters Ignoring 0

When working with raster datasets in ArcGIS, you may need to calculate the mean of multiple rasters while excluding zero values. This is particularly useful when zero values represent no-data or background areas that shouldn't affect your analysis.

Step-by-Step Process

Open your raster dataset in ArcGIS.
Use the "Raster Calculator" tool to create a new raster that identifies non-zero values.
Apply the mean calculation to the filtered raster.
Interpret the results considering the number of valid cells.

Note: This method assumes that zero values are truly no-data and should be excluded from calculations. If your dataset uses zero for meaningful data, you'll need to adjust your approach.

Common Use Cases

Environmental modeling where zero represents areas outside the study region
Land cover analysis where zero values indicate non-interest areas
Any spatial analysis where background values should be excluded

Formula Used

The mean of rasters ignoring zero values is calculated using:

Mean = Σ(Non-zero values) / Count of non-zero values

Where:

Σ(Non-zero values) is the sum of all raster cell values that are not zero
Count of non-zero values is the number of cells that contain non-zero values

Worked Example

Consider a 3x3 raster with the following values:

5	0	3
0	7	0
2	0	4

To calculate the mean ignoring zero values:

Identify non-zero values: 5, 3, 7, 2, 4
Sum of non-zero values: 5 + 3 + 7 + 2 + 4 = 21
Count of non-zero values: 5
Mean = 21 / 5 = 4.2

The mean of the raster values (ignoring zeros) is 4.2.

FAQ

Why should I ignore zero values in raster calculations?: Zero values often represent no-data areas or background in spatial datasets. Including them would skew your analysis toward these non-relevant areas.
What if my dataset uses zero for meaningful data?: If zero has meaningful values in your dataset, you should use a different approach like setting a custom no-data value or using conditional statements in the raster calculator.
How does this differ from the standard mean calculation?: The standard mean includes all values, while this method excludes zero values, providing a more accurate representation of the areas of interest in your dataset.
Can I use this method with multiple rasters?: Yes, you can apply this method to each raster individually or combine them first using raster math operations before calculating the mean.
What if all my raster values are zero?: This would result in a division by zero error. You should check your data for validity before performing calculations.