A map is a file which contains integer pixel values called object labels. The labels identify different objects in the image volume. Such maps are often the product of segmentation procedures.
If a label map has been loaded as image, contours of the objects can be obtained with the VOIs from label map button in the VOI tools panel.
The Step value of 1 usually works. The file is scanned and for each label found a contour VOI is created.
Illustrated below is the example of an atlas label file after contouring. Note that in this case the names are synthetically generated and have no relation to the anatomy.
At the end of this procedure the names can be edited and the VOIs saved.
An alternative for creating the label VOIs without loading the label map as image is described in Using Label Maps Files.