If I use an embeded google map in my website, will the data contained in an kml displayed be publicly viewable?
Will it be possible for the user to access just the data displayed (i.e., not the user interface) or would I have to provide that separately?
If you load your KML through the API, with GGeoXml(), (V2), or KmlLayer(), (V3), then your data needs to be in a public server because it is parsed by Google's servers and they need to be able to get to it. If you load it with a third party extension then you can keep it private.
Third party extensions that can load and parse KML data are EGeoXml() by Mike Williams
http://econym.org.uk/gmap/extensions.htm#EGeoXml
and GeoXml() by Lance Dyas
http://www.dyasdesigns.com/geoxml/
but I believe that both of those are only available for the API V2 for now.
I just upgraded my Google Maps JavaScript API Application from v2 to v3, following these instructions.
My v2 application was using the EGeoXml extension referred to by @Marcelo in the accepted answer to locally parse KML data.
A substitution of geoxml3 in its place, as suggested by @geocodezip (a contributor to the project) in a comment, functioned immediately in my v3 application.
No, the data will not be public. I'm not sure about your other question though.
来源：https://stackoverflow.com/questions/3435566/google-maps-kml-files