The Advanced Query Parameters field allow you to apply rules to the query that will be performed to populate the map, when using the Post Types and Meta Fields addon.
This field takes a JSON string that should translate to WP_Query parameters.
A popular use-case would be to display entries from a specific category/taxonomy. This would be done using this code:
This example above was taken directly from the documentation page, but converted to JSON format. It would only take entries from your post type, that are associated with the term
bob in the taxonomy
You can use any parameter that is accepted by WP_Query.
Make sure you use valid JSON, otherwise the parameters will not be applied.