NetRadar is a program that maps your Internet connection. Here are some images that it has generated over the past few years.
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Here is a map of a large Ethernet network.
This is an early beta of the new NetRadar  software. This screenshot was taken in early May.
This picture shows the ability of the layout algorithm to manually locate different parts of the network diagram. 
This is another visualization of the connectivity of a wide-area  network. 
Another view of the same data.
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NetRadar: Your Internet Spyglass.