A point layer must be loaded into ArcMap in order to use this
tool. If your point layer is an event theme and you are experiencing
problems, try making it a shapefile and trying again (right click on the
event theme in the Table of Contents, select Data, then Export Data).
Referencing unique values.
When you select a point layer from the drop-down list, the fields from that
layer are added to the lower drop-down list that allows you to select a
unique value field (to generate multiple MCP’s). Only fields that can
contain categorical data are added to this list (e.g. no fields with
floating point numbers are included). A field of the same type and size is
added to the MCP polygon layer and the unique values are copied for each MCP.
This enables you to Join the original point table and the new polygon table
together if you need to.
Using only selected features.
When you select a point layer from the drop down list the
program checks to see if there are 3 or more selected features in that
layer, and enables the "Use selected features only" option. If there are
less than three features selected, the option remains disabled (note that
you need at least three points to create a polygon).