Since the majority of geoprocessing tools take datasets as input and produce new datasets as outputs, most tool dialog boxes ask you where you want to write the output dataset. However, some tool dialog boxes will not ask you where to write output. The two primary reasons for this are the following:
- The tool doesn't create output datasets. For example, the Calculate Value tool writes the result of a numeric calculation as a message; the Spatial Autocorrelation tool writes results as a series of messages and, optionally, as an HTML file graphical summary. These types of outputs are accessible from the Results window.
- The tool modifies the input dataset. For example, the Add Field tool adds a new field to the input dataset and doesn't require an output dataset. The tools in the Editing toolbox all modify the feature geometry of the input dataset.
If you are unsure if you want to modify the input dataset, you can do the following:
- Make a backup copy of the input features, then run the tool using one copy as input, leaving the other copy in its original state.
- Start an edit session in ArcMap, then run the tool. From the ArcMap menu, you can use Edit > Undo or Edit > Redo commands to undo or redo changes made by the geoprocessing tool. When the edit session is stopped, the edits can be either saved (applied) or discarded.
- When input data is stored in a versioned database, tools will only modify the single version of the data. To apply changes to the rest of the database, the version must be reconciled and posted.
Another situation where a tool does not have an output parameter is when the tool has managed output. Managed output means the tool creates output but writes the output to a specific location. Only custom model tools that you create with ModelBuilder can have managed output. All ArcGIS Server tools (known as geoprocessing services) have managed output, because only the server can determine a suitable location to write tool output when the tool is run.
If you are building models to run locally (not as a geoprocessing service), you also have the ability to declare your model output parameters to be managed.
Managed outputs will be added to the display if you have check the Add results of geoprocessing operations to the display check box accessed with Geoprocessing > Geoprocessing Options.
Managed outputs can also be viewed in the result information posted to the Results window. The Results window allows you to copy and paste the tool's results to another location.