Summary
Quantile-quantile (QQ) plots are an exploratory tool used to assess the similarity between the distribution of one numeric variable and a normal distribution, or between the distributions of two numeric variables.
Discussion
When creating a chart object, optional arguments for the class constructor must be specified using the argument name; they cannot be specified by argument position. See the code sample section for an example of how to specify arguments using keywords.
Syntax
QQPlot (x, {y}, {showReferenceLine}, {dataTransformationType}, {dataTransformationParameters}, {title}, {description}, {xTitle}, {yTitle}, {dataSource}, {displaySize})| Parameter | Explanation | Data Type |
x | The field name for the x-axis variable. The field must be a numeric field. | String |
y | The field name for the y-axis variable, which is used to compare against the distribution of the x-axis variable. The field must be a numeric field. | String |
showReferenceLine | Indicates whether the reference line is visible in the QQ plot. True displays the line. False hides the line. | Boolean |
dataTransformationType | The data transformation type. Supported transformations are none, logarithmic, squareRoot, inverse, and boxCox. | String |
dataTransformationParameters | The data transformation parameters for the Box-Cox transformation. This parameter accepts a two-item list where the first item is the power parameter and the second item is the shift parameter. | List |
title | Sets the title of the chart. The title text appears at the top of the chart view and is used as the label for the chart in the Contents pane. | String |
description | Sets the description of the chart. The description text appears at the bottom of the chart view. | String |
xTitle | Sets the title for the x-axis of the chart. | String |
yTitle | Sets the title for the y-axis of the chart. | String |
dataSource | Sets the data source of the chart. When a chart is exported using the exportToSVG method or displayed in an ArcGIS Notebook, the data source is read and rendered on the chart. Valid data sources include paths to datasets, including local datasets, UNC paths, and service URLs, and arcpy.mp Layer objects. | Object |
displaySize [displaySize,...] | Sets the size of the chart when exported or displayed in an ArcGIS Notebook. | List |
Properties
| Property | Explanation | Data Type |
| dataSource (Read and Write) | Sets the data source of the chart. When a chart is exported using the exportToSVG method or displayed in an ArcGIS Notebook, the data source is read and rendered on the chart. Valid data sources include paths to datasets, including local datasets, UNC paths, and service URLs, and arcpy.mp Layer objects. | Object |
| dataTransformationParameters (Read and Write) | The data transformation parameters for the Box-Cox transformation. This parameter accepts a two-item list where the first item is the power parameter and the second item is the shift parameter. | List |
| dataTransformationType (Read and Write) | The data transformation type. Supported transformations are none, logarithmic, squareRoot, inverse, and boxCox. | String |
| description (Read and Write) | Sets the description of the chart. The description text appears at the bottom of the chart view. | String |
| displaySize (Read and Write) | Sets the size of the chart when exported using the exportToSVG method or displayed in an ArcGIS Notebook. The value must be specified as a two-item list, where the first item is the width of the chart and the second item is the height of the chart. | List |
| legend (Read and Write) | Sets the properties of the chart legend.
| Object |
| showReferenceLine (Read and Write) | Indicates whether the reference line is visible in the QQ plot. True displays the line. False hides the line. | Boolean |
| title (Read and Write) | Sets the title of the chart. The title text appears at the top of the chart view and is used as the label in the Contents pane on the List By Drawing Order tab | String |
| type (Read Only) | The string value indicating the chart type. | String |
| x (Read and Write) | The field name for the x-axis variable. The field must be a numeric field. | String |
| xAxis (Read and Write) | Sets the properties of the x-axis.
| Object |
| y (Read and Write) | The field name for the y-axis variable, which is used to compare against the distribution of the x-axis variable. The field must be a numeric field. | String |
| yAxis (Read and Write) | Sets the properties of the y-axis.
| Object |
.Method Overview
| Method | Explanation |
| addToLayer (layer_or_layerfile) | Adds the chart object to a layer or stand-alone table. |
| exportToSVG (path, width, height) | Exports the chart to SVG format. |
| updateChart () | Updates chart properties to sync changes between the object and the chart previously added to a layer. |
Methods
addToLayer (layer_or_layerfile)
| Parameter | Explanation | Data Type |
layer_or_layerfile | The chart will be added to the target object. The layer_or_layerfile argument can be a Layer or a Table object. | Object |
Often the final step after defining chart properties is to add the chart object to a layer or table using the addToLayer method.
Add a chart to an existing layer.
import arcpy
aprx = arcpy.mp.ArcGISProject("current")
map = aprx.listMaps()[0]
censusLayer = map.listLayers('Census Block Groups')[0]
# Add chart object to a layer
chart.addToLayer(censusLayer)exportToSVG (path, width, height)
| Parameter | Explanation | Data Type |
path | The path where the chart will be exported in SVG format. | String |
width | The width of the output graphic. | Integer |
height | The height of the output graphic. | Integer |
In some cases, you may want to save the chart as a graphic that can be shared and viewed outside of ArcGIS Pro. Exporting to the SVG graphic format is beneficial, as the chart elements and text are stored as vector elements that can be independently modified in a vector graphics software. An SVG graphic can also be resized to any scale without pixelation or loss in quality.
Export a chart that has a project layer data source to an .svg file.
import arcpy
aprx = arcpy.mp.ArcGISProject('current')
censusLayer = aprx.listMaps()[0].listLayers('Census Block Groups')[0]
# Set data source of chart object to a layer within current project
chart.dataSource = censusLayer
# Save the chart to file with dimensions width=500, height=500
chart.exportToSVG('populationByState.svg', 500, 500)Export a chart that has a feature service data source to an .svg file.
featureServiceURL = r'https://services1.arcgis.com/hLJbHVT9ZrDIzK0I/arcgis/rest/services/CrimesChiTheft/FeatureServer/0'
# Set data source of chart object to a feature service URL
chart.dataSource = featureServiceURL
# Save the chart to file with dimensions width=800, height=600
chart.exportToSVG('theftsPerBeat.svg', 800, 600)updateChart ()
Often the final step after defining chart properties is to add the chart object to a layer using the addToLayer method.
To further modify the chart properties, you can modify the properties of the original chart instead of starting from scratch with a new chart. You can then use the updateChart method to synchronize any changes into the chart that was added to the layer. This will allow the changes you make to be presented in the Chart properties pane and chart view.
Use the updateChart method to synchronize chart property changes into a layer.
chart.addToLayer(myLayer)
# Further modification is necessary
chart.description = "Data from the U.S. Census Bureau"
chart.updateChart()Code sample
Create a QQ plot using a layer name as the data source and export the plot to an .svg file.
import arcpy
chart = arcpy.charts.QQPlot(x="p_matter", dataTransformationType="squareRoot",
title="Comparison of Particular Matter and Normal Distribution",
dataSource="air_quality")
chart.exportToSVG("qqplot.svg", width=900, height=500)