Essential ArcPy vocabulary

This document introduces some vocabulary that is essential to understanding the ArcPy help.




ArcGIS 10 introduces ArcPy (often referred to as the ArcPy site-package), which provides Python access for all geoprocessing tools, including extensions, as well as a wide variety of useful functions and classes for working with and interrogating GIS data. A site-package is Python's term for a library that adds additional functions to Python. Using Python and ArcPy, you can develop an infinite number of useful programs that operate on geographic data.

ArcPy modules

A module is a python file that generally includes functions and classes. ArcPy is supported by a series of modules, including a mapping module (arcpy.mapping), a Spatial Analyst module (, and a Geostatistical Analyst module (

ArcPy classes

A class is analogous to an architectural blueprint. The blueprint provides the framework for how to create something. Classes can be used to create objects, often referred to as an instance. ArcPy classes, such as the SpatialReference and Extent classes, are often used as shortcuts to complete geoprocessing tool parameters that would otherwise have a more complicated string equivalent.

ArcPy functions

A function is a defined bit of functionality that does a specific task and can be incorporated into a larger program.

In ArcPy all geoprocessing tools are provided as functions, but not all functions are geoprocessing tools. In addition to tools, ArcPy provides a number of functions to better support geoprocessing Python workflows. Functions or methods can be used to list certain datasets, retrieve a dataset's properties, validate a table name before adding it to a geodatabase, or perform many other useful scripting tasks.

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