Selecting the right viewport?

I have more viewports laying one over another... on the lowest one i have some city map on middle I have hatches and on the topmost there are my buildings.

City map has the largest borders, while the other two vewports lies within its borders.

Now whenever I doubleclick inside citymap viewport border it goes into its paperspace. Even if I click into my buildings viewport.

Here is screenshot:

I sent citymap viewport to back. I dclick into "my buildings" viewport and it stil goes into "City map" viewport...

How can I go into "my buildings" viewport?

Thanks in advance...

Whilst you are in any of the viewports, hold down the CTRL key, and simultaneously press the R key to toggle between all your active viewports

Alternatively you can select the 'mybuilding' viewport & double click so it will maximise the viewport & will make it active as well.