To upload a KML file go to your Joomla backend -> Components -> Hotspots -> KML. Click on the new button and you will be presented with a screen similar to this one:
Provide a title, set the category where this KML should show. In the "KML file" field provide the kml file. In the description field enter a description of the KML. Once ready hit save.
Please note that your KML file size should not exceed the maximum upload file size that php allows. (To find that out you can go to Site -> System Information -> PHP Information -> upload_max_filesize)
The title, description, created by and date won't show anywhere on the page in the frontend. They are only visible in the backend.
Once you go to the category in the frontend - the KML file will be loaded automatically.
We give the file path to the google maps API and it takes care of actually loading the file and showing it on the map. The loading time can vary depending on file size and the upload speed of your site.
KML can only work on live sites! No localhost! The URL pointing to your KML files should be reachable through the internet.