In our iOS103 class we had a question about the image set properties dialog. On VSwin this allows the configuration of the image set's features, like adding support for iPad specific images.
What do the options "1GB", "2GB" etc mean?
With these an image set can be made specific to devices with 1GB of RAM, 2GB of RAM etc. For example a game could include higher resolution images for newer iOS devices.
Where is the option dialog on VSmac?
It does not exist :-( Image sets on VSmac always show all options (iPad, iPhone, ...), however some features like the 1GB, 2GB options are currently unavailable.
What is the entry field called 'on demand resources' for on VSmac?
This is for resource tags. A practical example of this might be if you tag all your resources on a per-level basis for a game. So you might have tags like "level1", "level2", "level3", etc. And this tagging system also allows you to specify a list of tags that should be pre-installed, so in the case of a game, you'd probably want level1 to be pre-installed. Another practical use-case might be if the app is multi-lingual and uses different images depending on the locale.
You can read more about image sets at: https://developer.apple.com/library/content/documentation/Xcode/Reference/xcode_ref-Asset_Catalog_Format/ImageSetType.html
Also note that all assets catalogs are really just JSON files. If a feature is not directly available in VS, you can always create asset catalogs in Xcode and then copy over the JSON file or edit the file by hand.