The critical infrastructure of the US is massive.  Here are six maps sourced through OpenStreetMap that show the array of six sectors of critical infrastructure.  When we talking about defending against physical and cyber threats to these sites, you can see just how impossible a task it is.

(Click each photo to enlarge.)

 

electric

Electric power lines

 

 

Bridges, including bridges in need of repair (in red)

Bridges, including bridges in need of repair (in red)

 

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Ports and waterways

 

 

airports-1480

Airports & Air Travel

 

 

rails-1480

Railways

 

pipes-1480

Pipelines