One of the most powerful features within Google Earth is the feature called the network link. The network link enables someone to tap into information in another file somewhere either on your local machine, or on a computer somewhere else on the Internet. The information can basically be anything the Google Earth files (KML files) can support. For example: Placemarks, lines, polygons, image overlays, and even 3D models. Network links also enable you to better handle KML files and keep the time it takes to start up Google Earth faster.
A network link simply points to another KML file somewhere. That file can be generated by a program running on another computer. The network link can automatically refresh based on a setting within the network link. You can update as fast as once a second, or just have it update once. You can also update network links based on when the user moves their view in Google Earth (this is called View Based Refresh).
Let me illustrate the power of the network link with some examples:
Global Cloud Map – this network link lets you automatically view a composite of satellite photos of the Earth’s clouds overlayed on the Earth. Not only that, but it automatically shows you the latest composite from a server which updates every 3 hours. If you store this network link in your My Places, every time you turn it on it will automatically have the latest photo (you must have an Internet connection obviously).
USGS Earthquake Monitoring – This network link automatically shows you the most current seismic activity – and summarizes activity during the last week with greater than magnitude 1.0. Read more about it here. Notice that the network link includes placemarks, lines, and a legend. Anything you can put in a KML file can be in a network link. This network link automatically updates (or refreshes) every 5 minutes.
3DWarehouse Network Link – This network link both presents to you the latest locations of 3D models at the Google 3DWarehouse, and also uses the feature of view based refresh. Depending on where you look, it will present you more information at that location. If you are zoomed further out it will show you a summary of models in different areas of your view. Zoom in closer and it will show you individual placemarks for each model in your view (if there are any). Read more about the 3DWarehouse network link here.
Besides providing the powerful ability to provide you with current and dynamic information, the network link can help you manage your Google Earth data much more efficiently. If you save a lot of your favorite KML files in your My Places it can slow down how fast Google Earth starts. This is because all the files in your My Places have to be loaded when you start. You can still keep pointers to all your favorite files, but keep the file size much smaller by using the network link. First, save each of your favorite KML content from your My Places to a file on your local machine, or, better yet, find the URL of the original file on the Internet. Then create a network link (menu “Add->Network link…“), and either put the local file location or the URL of the KML file in the Link field. Give the network link an appropriate name and description. Before you exit Google Earth, decide whether you want the network link turned on or not. Your My Places will now only be a couple hundred bytes for each network link and will only load more information if you leave it turned on the next time you start Google Earth. You can also have network links load other network links to reduce the size of your My Places even more. But, I’ll save tips on doing that for a future post.
More reading on the network link: