Okay, thank you.
So, there are no variables that return which collection your images are in, and due to the fact that an image can be in multiple collections and sub collections, it would be tough to make variables that work for everyone. For example, lets say I have A catalog with a collection called Parent with two sub collections: child1 and child2:
Image1 is in both child1 and child2
If we have a variable that returned the collections, should it just return "Child1, Child2"? Or "Parent >Child1, Parent>Child2"? Or "Parent>Child1, Child2"? I'm sure there are more things that would technically make sense but may or may not be what you want.
If I can suggest modifying your workflow, I think you'd be able to accomplish what you are trying to do without ever having to do the task of manually adding items to various collections by using Photo Mechanic Plus's Filters
For example, there are metadata fields specifically for the location where the image was created. If you populate these fields, you can then use Filters to get only the images from a specific location.
Of course, not every location name is unique. I'm in Portland, Oregon, but what if I have images from Portland, Maine? Filters take care of that. Filters act from the top down. If I choose something in the top filter, the number of items available in the lower filter gets adjusted. If you take a look at my attached screenshots, you'll see what happens when I have set up a Locations Shown > State and then City filter. If I don't click on a state, I see all of cities in my catalog, but once I do click on the state, I only see the cities of the images where images have that state in their metadata. If you happen to have a device that puts the GPS coordinates into your images (or you add them later in Photo Mechanic), you don't even really need to enter the location information, reverse geocoding can do that for you. And obviously you'd not want to have to set these filters up each time, so using the Snapshot function (the little flashbulb button at the top of the filters) lets you save a filter with a name, so once you set up your filters, save a snapshot to be able to pull up that set of filters again later.
I'm not sure what's in your other collections, as you've only really discussed location information so far, but I assume "When" has to do with Date and Time, which you can Browse or Filter by, and you'd be able to set up an appropriate set of filters for the collections have under the Event collection. I'm assuming "All" is just a collection of all items in all catalogs? You can pull up a contact sheet with every item in all catalogs by doing a Catalog Search for the period character (.)
I understand that this is a departure from your current workflow, but I hope you are able to employ some of these suggestions in your use of Photo Mechanic Plus