The design guidelines for Apple IOS are a bunch of different rules and concepts to give the interface of Apple products that distinctive polished apple feel. They’re also very useful for app designers who are looking to make apps for Apple devices. Here are the main concepts behind the guidelines.
For example, here are some guidelines for the iPhone X on how to layout an app. If an app didn’t comply with these rules, like if it had a video in the Status Bar, instead of the Layout Margin, then it probably wouldn’t be allowed on the Apple App Store because it would be hard to use, and just wouldn’t look right.
There are also very specific design rules for the visual layout on different apple devices. All of these ideas blend together to create a seamless experience for users.
Looking at the Mac that I’m currently using, I can clearly see the different aspects of the guidelines that have been used, for example, the options bar at the top of the screen, that I can also see in the guidelines example above. Here’s a screenshot that I just took. The design is clean and simple, and easy to look at and navigate. Well, it would be if it was its proper size because at the moment it is tiny and very hard to see.
The only problem with making apps for Apple devices is that they are extremely strict with what they allow on their App Store; if an app somehow doesn’t meet the very high design expectations, then they will deny it. They are so strict about this because they want users to have a polished experience, and to feel like they have the best of the best right at their fingertips. Apple feels like this would be completely ruined by apps that went against their many, many design guidelines.
Research
https://developer.apple.com/design/human-interface-guidelines/ios/overview/themes/