Global Mapper provides a number of tools for creating and editing data. When these various edits or data creations are performed, there are a few different ways to undo the edits.
Reload the data
Global Mapper does not modify the original data that was loaded from the external file. When edits are performed, the workspace stores the information about the loading of the original file, and then any modifications that are made to the data. In some cases, the best way to undo edits is to remove the layer, and reload the original data. Another option is to save the workspace before making edits, and then if the edits are undesired, do not save, and reload the original workspace.
Rerun the operation
Many of the Analysis and Layer tools create a new data layer. While it is not possible to explicitly undo the operation, it is possible to remove the new layer that was created. Then if desired, rerun the operation with different settings.
During some operations, like drawing new features, you can undo your last placed point by pressing Ctrl+Z. There is not currently a way to reverse most digitizer operations. See below for the restore option to revert data back to the last saved form.
Features that have been deleted, or modified in a way that they are replaced my new features may still appear as part of the deleted features in a layer. For more information on rendering and then undeleting features see Deleting and Undeleting Features.
If the changed made after moving or modifying the shape of an area or line feature are undesirable, it is possible to restore the feature to its original shape. Simply select the feature(s) with the digitizer tool, and select the Restore Original Shape from the right-click context menu or the top-level Digitizer menu. This will revert the feature back to the original version.