If you store the major areas and the products for those areas in custom database tables you'd be able to use CB Query Field to pull the custom values into a dropdown select. You'd then use CB Core Fields Ajax and its Update On functionality to refresh the products select when the major area select changes value. This would ensure the products would always be relevant to the area selected. Update On functionality is in CB Query Field, but it's no longer being further developed and will be removed so you could use that without CB Core Fields Ajax, but I do not recommend it as it will go away in a future release.

An alternative would be to just make all of your select fields manually then use CB Conditional to show/hide the relevant product select fields based off the major area selected.

Depends on how you want to do it. If using custom database tables with CB Query Field and CB Core Fields Ajax you'd just have 2 fields. The area and the products. When selecting an area it'd update the products displayed as you'd write your database query to check the value of the area field. If using CB Conditional you'd just be showing/hiding the relevant products field based off the value of the area field and will need as many product fields as you have area select options.

Multi-select and multi-checkbox fields always store in the database as |*| delimitered. Use LIKE in your SQL to match values inline or use SQL functions to split the |*| into comma delimitered list which you can use FIND_IN_SET to search.