In this method, we return the column names that are required for the styles to draw the feature properly. For example, if you have a style that colors areas blue when a certain column value is over 100, then you need to be sure you include the column name. This will ensure that the column data is returned to you in the feature when it is ready to draw. In many of the styles, we add properties to allow the user to specify which field they need; then, in the GetRequiredColumnNamesCore, we read that property and add it to the collection.