A compact and congested city center sits atop a spaghetti pile of underground pipes and wires and more.

Here are ten things you might find below the pavement in Manhattan:

1. Con Edison’s 105 miles of steam pipes heating nearly 2,000 buildings. (Take care – it’s 350 degree heat!)
2. Water mains. Many lead to buildings. Others to fire hydrants or drinking fountains.
3. Electrical conduits and telecommunications infrastructure.
4. Natural gas mains. Beware of the pressure.
5. Sewage pipes. These have to run downhill in the end.
6. Storm drainage. Ditto.
7. Underground storage tanks containing things like Freon or fuel oil or industrial chemicals. Who knows what else.
8. History, from cobblestones and Colonial foundations to bottles and bones.
9. Passenger and freight train tunnels. Think PATH, Metro North, and the Long Island Rail Road when they roll into Penn and Grand Central stations.
10. Subway tubes and stations and the air vents that support them. The city has 275 fully underground stations.

What’s actually down there often remains a mystery, even to public and utility officials. What happens when a corroded pipe bursts?

The Big Apple isn’t the only North American city to have a subway system. Underground rapid transit is a defining quality for a great metropolis, after all. Here are ten related facts.

1. A shared dream: Two brothers – Henry Melville Whitney in Boston and William Collins Whitney in Manhattan – vied against each other to create the first public subway system in North America. Boston won in 1897. New York’s opened in 1904. Who says sibling rivalry doesn’t have its place?
2. Chicago: While the Windy City is known for its “L,” those elevated tracks running in a loop through downtown, Shy-town also has a portion operating underground. That was a late entry, though, opening in 1951.
3. Washington: Opened in 1976, the spick-and-span Metro has 117 miles of route, six lines, and 91 stations. It’s the third busiest rapid transit system in the country. Just don’t get caught snacking en route to work.
4. San Francisco: The Bay Area Rapid Transportation system has six lines connecting 112 miles of route and 48 stations. It carries an average of 423,000 riders daily. Opened in stages from 1972, it was hailed for its technological advances. And then for its glitches.
5. Philadelphia: SEPTA’s modes include about 25 miles of underground route in the center city, mostly as the Broad Street Subway, opened in 1928, and the Market-Frankford Line. As for safety? It’s far less terrifying than those Jersey drivers across the Delaware.
6. Cincinnati: Abandoned tunnels and stations from the city’s efforts to build an underground rail system haunt the city. Construction halted during World War I and was officially cancelled in 1928 but bonds for the project weren’t paid off until 1966. Some fans say the failure to complete the dream caused Cincy to fall from the front ranks of American cities – traffic congestion remained a big headache until Interstate highways brought some relief.
7. Montreal: Canada’s busiest system opened in 1966, running on the then innovative rubber tires. Le Metro now has four lines, 68 stations, and 43 miles of routes serving an average of 1.3 million riders daily – third highest in North America.
8. Toronto: Opened in 1954, the TTC has an average of 915,000 daily riders on its four lines, 48 miles of route, and 75 stations. Its Yonge-University Line has a U-shaped route. Two others run east-west, while the fourth heads north and then turns east.
9. Mexico City: The second-busiest in North America, with an average 4.6 million riders daily, it opened in 1969 and now has 12 lines and 124 miles of route. It’s likely the most colorful system on the continent.
10. Los Angeles: Metro Rail, which opened in 1990, has two lines operating fully underground. They run 36 miles and have 22 stations. They carry an average of 153,000 riders daily – a low figure that stymies observers, considering the region’s notoriously jammed freeways. But poor connecting bus service may be part of the problem.

Opened in 1904 and the second-oldest system in the country, the New York subway is the biggest and busiest in North America.

Here are ten facts for perspective:

1. Riders: 5.58 million on a weekday. (OK, even if most of them are probably using it at least twice, coming and going, that’s still over two million people. The busiest time is between 7 and 8 a.m.)
2. Top speed: 55 mph.
3. Average speed: 17 mph.
4. Average voltage in the third rail: 625 DC.
5. Route length: 245 miles.
6. Total track length: 850 miles. (Remember, a route requires two tracks, one in each direction. And where local and express routes overlap, you can double that. Stretched out, the track would run well past Chicago.)
7. Daylight: 40 percent of the track runs above ground, mostly in three boroughs outside Manhattan. (It doesn’t run on Staten Island.)
8. Two sizes of cars in operation: The IRT tunnels, curves, and stations are too small for the cars running on the IND and BMT lines.
9. Directions: The current official map by Michael Hertz Associates dates from 1979. It is not geographically accurate but makes Manhattan larger to accommodate for the borough’s having the most services. The earlier 1979 subway map by Massimo Vignelli is considered a modern classic but is flawed by its placement of geographical elements.
10. Men working: Because the system does not shut down overnight, all track maintenance occurs while trains are running. It can account for delays and rerouting, as needed. (Well, some of them did inspire my novel now running as Subway Visions.)