GeoJSON data contains many properties which can result in large object size. When dealing with large collections of GeoJSON objects in your FileMaker solution, your file size can increase significantly, causing everything to crash. Learn how to handle a large JSON collection in your FileMaker solution quickly and efficiently with this demo file on importing prepared values.
Read my blog post to learn more about how to use the demo file. 
Hello, I have just download the demo, very good technique,
but when you try to repeat the process it says that the file is in used or locked.
Thanks for reporting that. Are you able to tell if that’s a record lock on FileMaker that you’re seeing, or a filesystem lock on the sample data? If the latter, which OS are you using? It could be that you might run through in the script debugger, and see if there is a native file handling script process which is creating a file handle, but isn’t releasing it before the script finishes running. Any further pointers you have to reproduces are appreciated.