At peak hour at key stations trains will run literally every 1 - 2 minutes. (femaletravelbloggers.com)
Teleconnections are best defined by values over a grid but it is often convenient to devise simplified indices based on key station values. (ipcc.ch)
Linking central London and key stations en route with all Heathrow Airport terminals, Heathrow Connect carries passengers from London's Paddington station to Terminal 4 in only 33 minutes and terminals 1,2 and 3 in just 25 minutes. (thetravelmagazine.net)