Raster Statistics

Statistical charts are powerful spatial data analysis tools. They present attribute data from geographic data in an intuitive non-map chart view, helping you identify hidden patterns, trends, and relationships in the data.

Create a Statistical Chart from a Raster

The raster statistics tool creates charts from raster layers that have an attribute table, including standalone tables. To create a chart from data that is not yet in the map, add the layer to the map so it appears in the Layers list on the left.

Steps:

• Select a raster layer in the Layers list.

• In the raster toolbar, select Create chart.

• In Chart properties, select the variable value.

Chart window: The chart window appears on the right side of the view. In this window, you can define chart variables, set the transformation method, specify the number of bins, and view statistics.

Parameters:

• Variable

  • Numeric value: A histogram requires one continuous numeric variable on the x-axis.

  • Transformations:

    Transformation mode	Description	Recommendation
    Log transformation	A log transformation is usually used for positively skewed data where some values are very large. If these large values are present in the dataset, a log transformation can help make the variance more constant and normalize the data.	A log transformation can only be applied to numbers greater than zero.
    Square root transformation	A square root transformation is similar to a log transformation because it reduces right skew in a dataset. Unlike a log transformation, it can be applied to zero.	A square root transformation can only be applied to numbers greater than or equal to zero.
    Box-Cox transformation	Applies a power function to normally distributed values.	A Box-Cox transformation can only be applied to positive values.
    Reciprocal transformation	Calculates the reciprocal (1/x) of each value (x) in the field.	A reciprocal transformation cannot be applied to zero. If a field contains zero values, those values are evaluated as null values.

• Standard normal distribution: Applies a standard normal distribution based on the selected transformation.

• Bins

  • Number of bins: The number of bars. Changing the number of bars lets you view more or less detail in the data structure.

• Statistics include mean, median, standard deviation, count, maximum, minimum, and other values.

Update Raster Statistics

Update raster statistics, usually shown as Update statistics on the toolbar, recalculates statistics for the selected raster layer and refreshes charts and related views.

When to Update

• After cell editing, such as setting NoData, setting constants, interpolating, or filtering, when you need the statistics to match the current raster content.
• When the histogram or statistics do not match expectations after creating a chart and need to be recalculated.
• After the imagery extent, displayed band, or data changes, when you need updated minimum and maximum ranges for more accurate rendering or stretching.

Updated Items

After the update, iXGIS refreshes basic statistics by band. Common statistics include:

• Minimum and maximum
• Mean and standard deviation
• Histogram, used to display the value distribution

For single-band rasters that are more like classified or discrete-value rasters, iXGIS may also calculate and update:

• Unique values and their cell counts. If there are too many unique values, unique value statistics may be skipped.

Steps

1. In the Layers list, select the raster layer whose statistics need to be updated.
2. In the raster toolbar, click Update statistics.
3. Wait for the calculation to complete.
4. Return to the chart window or layer information panel and review the refreshed statistics.

Notes

• Statistics calculation may take a long time for large, high-resolution rasters.
• Updating statistics does not modify raster cell values. It only updates statistical results and related cache information.
• If there are too many unique values to calculate unique value statistics, try adjusting the unique value statistics limit in User options > Raster, or use a histogram to view the distribution.