I just spent a couple of hours figuring out how to split a route in Mac BaseCamp, including a fruitless call to Garmin support ("Oh yeah--the Windows and Mac versions are identical. Just select the Split tool"). I'm posting this thread in the hopes that it will save other folks from the same frustration. Route and track splitting isn't intuitive, and it isn't well-documented. But, here's how it's done in BaseCamp v. 4.4.7:
First, scroll the main window until your split point comes into view. Hover the cursor over the point where you want to split your route or track. A callout will pop up, and the top item in the callout list should be the routepoint/trackpoint number of the split-point. Make note of that number.
Next, double-click the route or track item in the 'list contents' pane in the sidebar on the left side of the main window. A route/track editor will open, with a list of the points in the route or track you selected. Scroll down to your split-point (using the number from the preceding step) in that list and select it in the editor.
Finally, in the lower-left corner of the editor window, there is a gear icon. Click it, and select 'Split Route' or 'Split Track', as the case may be, from the menu that pops up. The route or track will be split at the point you selected.
In conclusion, I'd like to drop down on my knees and beg Garmin to pleeease add the editing tools from the Windows version of BaseCamp to the OS X version. In Windows, I simply selected the Split tool from the toolbar and clicked on the split-point. I'm off to take a couple of aspirin now...
