Similar to Merge Fields are Interest Groups. These are identifying characteristics you can use to create segments in MailChimp and send targeted emails to users with specific interests. (See: Getting Started with Groups)
Mapping is similar to Merge Fields, but an interest in MailChimp can have more than a single option. For example an interest can be a multiple option checkbox, a single checkbox, a select field, or a radio group.
Using groups is optional, but if you do use them there are some important considerations to make sure your mapped fields will correctly pass data between the two applications.
It is very important to point out that MailChimp and WP-Members handle these types of fields in a different way. In order for your information to pass between the two applications, the “saved” value of the data needs to be EXACTLY the same.
In MailChimp, select, checkbox, and radio field types use the same value for displaying the option as they do for saving. So if the option displays as “Kayaking”, then the saved value will be “Kayaking”.
WP-Members offers you the option to define a display value for the selection and a saved value. For multiple checkboxes and multiple select fields, these are in the format “Display value|saved_value” – or using our kayak example above, “Kayaking|kayaking”. The displayed option for selection would be “Kayaking” and it would save as “kayaking”. In most cases, these values can be the same. So when creating a field for identifying an interest group in MailChimp, it is probably a good idea to create the same display value and saved value, and make sure they are the same as your MailChimp interest group field. So in this case, in your WP-Members field it would be “Kayaking|Kayaking” (same for display and saved value) so that the saved value that is passed is the same as the MailChimp value. Remember, case sensitivity counts, too.