The “Calculate Field” tool in ArcGIS Pro allows users to execute both simple and complex calculations, applying them to text fields as well as numerical fields. These operations can be run across the entire layer or only on selected rows, depending on the user’s needs.
To calculate the percentage that each polygon represents in relation to the total area of a layer, such as “plant_cover”, it is first necessary to determine the total area. This is done by opening the attribute table, right-clicking on the “Area” field header, and selecting either the “Explore Statistics” or “Visualize Statistics” option.
In the statistics window, the “Sum” value represents the total area of all polygons in the layer. This number can be noted or copied using “Ctrl + C”.
To proceed, a new field must be created to store the calculated percentages, such as “Percentage”. Once created, right-click on the header of this field and select the “Calculate Field” option.
In the expression box, use the formula: !Area! * 100 / total_area_value. In this expression, !Area! refers to the field containing each polygon’s area. This field can be inserted by double-clicking on it in the “Fields” section of the calculator interface.
The “Explore Statistics” function also enables the creation and configuration of charts. This can be done by clicking the “Create Chart” icon, located to the right of each field in the statistics panel. This functionality provides an overview of the data distribution and supports further interpretation.
Creation and configuration of charts using the “Explore Statistics” function
Expressions can include various mathematical operations such as addition, subtraction, multiplication, and division. Parentheses may be used to control the order of operations. Users can write expressions in VBScript, Arcade, or Python.
Operations with “Calculate Field” in ArcGIS Pro.
For advanced calculations or access to geoprocessing functions—such as those involving geometry—it is recommended to use Python. This scripting language provides extensive capabilities and flexibility for custom expressions.
For further reference, ArcGIS Pro offers a section titled “Calculate Field Python examples” in the official help documentation. This resource provides a wide range of sample expressions and detailed explanations to assist users with more complex calculations.