Data types for geoprocessing tool parameters

Geoprocessing is built around the concept of data types. Every tool parameter has an associated data type that defines the contents of the variable. Some simple data types are string (any set of alphanumeric characters), Boolean (a true/false value), and long (an integer value between -2,147,483,648 and 2,147,483,647). In addition to these simple data types, there are dozens of other data types built specifically for data found in ArcGIS, such as field, coordinate system, and extent.

Documentation for each data type is found in Geoprocessing_data_types.pdf. If this link doesn't work, you can open the document (Geoprocessing_data_types.pdf) from the \arcgis\Documentation folder in your ArcGIS Desktop installation location.

To view this document, you need a copy of Adobe Reader, which you can download free from

Where data types are needed

Casual geoprocessing users don't need to know about data types. But there are situations where you are asked to provide data types for variables and parameters.

In the case of ModelBuilder, most of the time you create variables from an existing tool parameter. Since all parameters have an associated data type, the variable is automatically created with the correct data type.

Determining a parameter's data type

There are several ways to determine the data type of a parameter:

String syntax

Every data type has a string syntax used in the tool dialog box and in scripting. Most data types have a very simple string syntax, such as the path name to a dataset, a number, or a keyword. For example, the field data type is the name of the field. Other data types have more complex syntax.

The string syntax for a data type can be found in the PDF file described above. If you are unclear of a particular string syntax for a data type, you can try this:

  1. Locate a tool that uses the data type.
  2. Execute the tool using its dialog box.
  3. In the Results window, right-click the result and click Copy as Python snippet. You can then paste this snippet into any text editor (or the Python window) and examine the string values of all parameters.

Data types and scripting objects

The string syntax of some data types is too complex to use in a script. For example, here is the text string for the spatial reference data type that defines an Eckert IV coordinate system:


For data types with complex strings, arcpy contains classes with methods and properties that allow you to easily create and modify the data type. For example, see the SpatialReference class.