running El Capitan 10.11.1 - will secure format hard drive and reinstall OS X wipe out Aperture?

Yes it will. Not entirely sure what you mean by secure format, but partitioning/formatting or simply erasing the hard drive will delete everything on it. Reinstalling the OS will be just the OS.

If you have an older version of Aperture, it may no longer re-install as it is no longer supported. Mine still works, but it's been installed for several OS versions and it still works in 10.11.x

Yes, a secure format will wipe out EVERYTHING. Assuming you have been backing up the computer you can restore the apps and data you want. If you have not been backing up then back it up immediately using either Time Machine or create a bootable clone using either SuperDuper or Carbon Copy Cloner. You will need an external HD to do either backup.

Dave in Cincinnati wrote:

Thank you. I am not aware if you can see my other response but your reply helped me as well. I do have an external hard drive and regularly use Time Machine. I will take some extra steps before transitioning my old iMac to my son. Thank you again.

If you already have a Time Machine backup then you are pretty much set. When you get a replacement Mac you can restore Aperture and it's library to your new machine from your old TM backup.

Ahh, since you intend to gift your Mac, you'll need to check the licensing agreements - anything (OS or app) downloaded from the app store is NOT transferable and you must remove it from your machine. So, if yours came with install disks, use those to wipe the drive and reinstall the original OS; if it came with Lion or later, use internet recovery (Command + Option + R) to wipe the drive and reinstall the original OS.

If you purchased Aperture on retail disks, you can give/sell those, but you are not allowed to retain a copy. If you purchased it from the app store, the license is for you only and not transferable.

Here is the licensing agreement for El Capitan:

http://images.apple.com/legal/sla/docs/OSX1011.pdf

Applicable in this situation: Sections 2A and 2B, and 3A and 3B.