📏 Auto-Add Area and Length Fields in a Geodatabase Using ArcPy

 

📏 Auto-Add Area and Length Fields in a Geodatabase Using ArcPy

When managing spatial data in ArcGIS, calculating geometric properties like area or length is a common requirement—especially for analytics, reporting, or quality control.

In this post, you'll learn how to write a Python script using ArcPy that automatically adds:

• a CALC_AREA field to all Polygon feature classes

• a CALC_LENGTH field to all Polyline feature classes

All within a given File Geodatabase (.gdb)—whether the feature classes are inside datasets or at the root level.

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🧾 The Script

python
import arcpy
import os

# 📍 Set your input File Geodatabase path
input_gdb = r"C:\Path\To\Your\DataModel.gdb"

# Set the workspace
arcpy.env.workspace = input_gdb

# 🔍 List all feature datasets (or include root-level FCS by using [''] if none)
datasets = arcpy.ListDatasets(feature_type='feature') or ['']

# Loop through all datasets and standalone feature classes
for dataset in datasets:
    dataset_path = os.path.join(input_gdb, dataset) if dataset else input_gdb
    feature_classes = arcpy.ListFeatureClasses(feature_dataset=dataset)

    for fc in feature_classes:
        fc_path = os.path.join(dataset_path, fc) if dataset else os.path.join(input_gdb, fc)

        # 🧠 Get geometry type (Polygon or Polyline)
        desc = arcpy.Describe(fc_path)
        geom_type = desc.shapeType.upper()

        # 🏗️ Define field to add based on geometry type
        if geom_type == "POLYGON":
            field_name, field_type = "CALC_AREA", "DOUBLE"
        elif geom_type == "POLYLINE":
            field_name, field_type = "CALC_LENGTH", "DOUBLE"
        else:
            continue  # Skip Points or unsupported types

        # ✅ Check if field exists before adding
        existing_fields = [f.name for f in arcpy.ListFields(fc_path)]
        if field_name not in existing_fields:
            arcpy.AddField_management(fc_path, field_name, field_type)
            print(f"✅ Added field '{field_name}' to '{fc_path}'")
        else:
            print(f"ℹ️ Field '{field_name}' already exists in '{fc_path}', skipping.")

print("\n🎉 Geometry field addition complete.")

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🛠️ How It Works

• ListDatasets() gets all feature datasets in your geodatabase.

• ListFeatureClasses() gets each feature class inside them (or in the root).

• Describe() helps us detect if a feature class is a Polygon or Polyline.

• If the appropriate field (CALC_AREA or CALC_LENGTH) is missing, it gets added as a DOUBLE.

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📦 Why Use This?

• You're preparing data for area/length calculations.

• You want to standardize schema across multiple datasets.

• You're doing bulk data migration or preparing for a data audit.

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✍️ Bonus Tip: Calculate Values

If you'd like to calculate values right after adding the field, insert this below the AddField_management line:

python
if field_name == "CALC_AREA":
    arcpy.CalculateField_management(fc_path, field_name, "!shape.area!", "PYTHON3")
elif field_name == "CALC_LENGTH":
    arcpy.CalculateField_management(fc_path, field_name, "!shape.length!", "PYTHON3")