The vector layer must be loaded into ArcMap before starting this tool. This layer must contain a unique ID field that
identifies the subsets you wish to sample. For instance, if you are randomly selecting a certain number of polygons
of each landcvoer type from a landcover layer, then the unique ID field would be the field containing the landcover codes,
not the polygon ID field.
Creating the random selection
Users may specify either a constant number of features to select, or a percentage. If the constant number you supply is equal to
or greater than the number of features in any one of the subsets, then all the features in that subset will be selected. For instance,
if one of the subsets contains 35 features and you enter 40 as the number of features to select, the resulting selection will
contain all 35 of the selected features, and it will not inform you that it was unable to select 40 (so you need to be cognizant
of how many features you have).
Writing the RNDSELSS field
If you check the option to add or update this field with the new selection then it is important to realize that any previous RNDSELSS
field will be overwritten, and that the tool will fail if you do not have write permissions to that attribute table.