Hi gonfish,
I'm not sure if we're just having a problem with terminology or if you still misunderstand the use of the map selection tool. As Terry said, if you zoom out so you can see a larger area of the map you will see that there are lots and lots of smaller selectable areas in Ibycus topo (and most map products). You select and deselect by simply clicking on the areas you want to select. First click turns them pink (selected). Another click on the same area deselects it.
You can select multiple "tiles" by clicking, holding and dragging a rectangle over the larger area to select multiple tiles at once.
You can deselect multiple tiles by holding the CTRL key down and clicking an dragging the rectangle over the tiles you want to deselect.
As Terry said, if you click on the MAPS tab you can see all the individual map tiles you have selected and you can deselect them by clicking, CTRL-clicking or SHIFT-clicking and then hitting the delete key. When you look at the MAPS tab, down at the bottom you can see the number of tiles you have selected and the amount of memory that will be needed to load them onto your device or memory card.
If you get completely fouled up and confused you can simply exit Mapsource, do NOT save your work, and restart Mapsource. It will come back up clean and you can start from scratch.
...ken...