However, if you do this and include the header to the subfolder with 'include("../header.php");', it will include that file. The issue is that the default path for the the files in the subdirectory will not link up because the path takes on the folder of the file in the new-york directory.
Luckily, there is one easy trick to allow everything to work flawlessly, thus, you only need one file in the new-york folder to utlize all css, images and js of the root folder. The simple line of code is the self closing base tag. An example is shown below with a line of code that can be added to the file in the new-york directory.
Do note that placement is critical. It should be positioned above all links to css and js; otherwise any links above it will use the path in the current directory. Both examples shown below will work.