Do I need to use a memory card to create Quickdraw Contour Maps?

I'm heading out with the unit for the first time (Striker Vivid 9sv) this coming week - I'd really like to create some maps on the small local lakes I fish. 

1. Do I need an SD card added to the unit to save Quickdraw Contour Maps? 

2. If I create a map in an area where I already downloaded data from the Quickdraw Community - will my map MERGE, or OVERWRITE the existing, downloaded data?

Thanks!