It's not where in the project but rather the type of the file that controls this. For many types of non-source-code files Xcode just copies them to the root of the bundle. If you look at the Build Phases > Copy Bundle Resources build step you'll see all the files that are copied into your bundle.
You can print out the full paths to these files when your app launches or open up the app bundle in the Finder to see where these files are.