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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This is a visualization of a large network with several enormous Ethernet segments (the fan and circular structures) .
More large scale LAN  topology. 
This graph shows a topology where (on the right) network segments are doubly connected to a main backbone on the lower left part of the screen.
This is an experiment in the removal of the core of a graph. The resulting autonomous segments may be used in the future for topology compression.
Here is an experiment displaying network topology based on low round trip time measurements.
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NetRadar: Your Internet Spyglass.