I generate KML files which may have 50,000 placemarks or more, arranged in Folders based on a domain-specific grouping. The KML file uses custom images which are packed in to a KMZ file.
I'm looking to breakup the single KML file in to multiple files, partitioned based on the grouping, so rather than having 1 large document with folders, i'd have a root/index KML file with folders linking to the smaller KML files.
Is this possible though? I think that a KMZ file can contain only 1 KML file, regardless of where it's located or its name, in the zip. Furthermore, I'm not exactly sure how a KML file can link to another KML file. Is the only way to have it as a <NetworkLink> to a local file? Can a <NetworkLink> work to link to a file local in the same KMZ?
Yes you can use a networklink to accomplish this and as far as I know it's the only way to do what you ask. And yes you can reference local files in Network links
See: http://code.google.com/intl/nl-NL/apis/kml/documentation/kml_tut.html (search for "Network Links") where it says:
A network link contains a element with an (a hypertext reference) that loads a file. The can be a local file specification or an absolute URL. Despite the name, a <NetworkLink> does not necessarily load files from the network. The <href> in a link specifies the location of any of the following:
• An image file used by icons in icon styles, ground overlays, and screen overlays
• A model file used in the element
• A KML or KMZ file loaded by a Network Link
No you can't reference to another file inside a kmz. A kmz can only contain 1 kml file (it can contain other type of files though) You can find the layout of kmz files and what may be put in them here Specifically note the following section:
2.Put the default KML file (doc.kml, or whatever name you want to give it) at the top level within this folder. Include only one .kml file. (When Google Earth opens a KMZ file, it scans the file, looking for the first .kml file in this list. It ignores all subsequent .kml files, if any, in the archive. If the archive contains multiple .kml files, you cannot be sure which one will be found first, so you need to include only one.)
One final remark is that your question doesn't tell anything if you need these 50.000 placemarks as offline files or not. If you could serve them dynamically you could use the region based links where GE will tell you the viewing region of the client so you can return a small subset of the waypoints (only the ones that are inside the users view) For more info this is the link to click on.