I think this is what you're asking. Zoom into the part of the map you want to select. Click the "Select" arrow in the toolbar. Drag a box around the tracks you want to select. Those tracks will now become selected on the map and highlighted in the data view pane on the left.
I have a lot of GPX files imported into BaseCamp and now I want to select a part of the map and see all the tracks in that region.
Is it possible at all in BaseCamp?
I think it only displays the selected item in your route at one time. So if you have all your stuff in My Collection, you have to select My Collection to see all the routes.
