Saving File Changes on External Drive

To save space on my MacBook air, I backup and access my Iphoto library to/from an external drive.

Please explain - backing up is totally different from accesing - exactly how are you "backing up" and exactly what do you mean by "accessing"

When I make changes to the library (for example, a new album) are these changes automatically created and saved to the external file, or do I need to "re save" the whole file each time?

All changes you make are made to (and only to) the currently active library - no matter where it is located - If you are using your iPhoto library on an external drive then that is where your changes are being kept - if you are using an iPhoto library on your main drive then that is where the changes are being made

If (and it is not at all clear) you are using an iPhoto library on your main drive and then backing it up to an external drive the backup program and method you use determines what is being done and when it is being done - for example Time Machine in its default mode would backup all changes every hour

Remember we know nothing about yoru system or procedures and can only work with the information you give us

LN

I went to the Iphoto Library file in Finder, selected it, then moved the file to my external hard disk drive, which has a 500GB capacity. So, even though I called this "backing up" maybe it was "copying" - but I do not understand the difference.

A backup is a copy on a different device - so copying to an external device is a backup - UNTIL you start using that copy as your library - then it is the library and you have no backup -- and note that if you do not have a backup you are 100% guarenteed to lose all of yoru photos sooner or later - computers, software and people fail and when they do a current backup is the only thing that will save your photos and other files

Finally, I re-opened Iphoto, and when it asked me to select a Library, I chose the library file that I had copied onto my external hard drive. All of my photos then re-loaded into Iphoto, and I have been looking and them and selecting some for deletion.

So when you did this you started using the iPhoto library in the EHD and everything you do is reflected there

I believe I understand what you've said - that changes I make (whether deleting, renaming, cropping, etc.) to photos in this file are being made directly onto the external hard disk drive.

Yes

So, to be absolutely specific, when I delete a photo in Iphoto to the TRASH CAN and then EMPTY the trash can, this photo is now and forever GONE from the external hard disk drive.

Maybe

To delete from iPhoto when using a default "managed" library (the iPhoto preference to "copy imported items to the iPhoto library is in its checked state) drag a photo from an event to the iPhoto trash (or select it and press delete) and then empty the iPhoto trash and with iPhoto '11 under Lion empty the system trash - then the photo is gone forever from the external hard drive

And edits I make to photos are SAVED to the external hard disk drive. IS THAT CORRECT?

Yes

LN