Items on and off the radar screen

It was a snowy December here in Boston, during which one storm seemed to blur in with the next. And having been out of town at a critical juncture, the Night of the Very Long Drives Home, Dec. 13, I somehow lost count of which storm was which after that.

Then one day, when I heard a radio host report that such-and-such storm was "still on the radar," I did a little double take.

I realized he meant it literally. He, or at least someone who was supplying him with information, had an actual radar screen. It was one of those moments when the literal and the figurative were one, in a kind of harmonic convergence.

I, on the other hand, had no such fancy hardware. I had a memory bank, and one that had not been supplied with a completely wonderful wad of data at that.

A radar screen, with its characteristic "sweep," is such a good metaphor for the idea of a comprehensive overview of whatever one is trying to follow that I wonder how people got along without it as a source of metaphor before radar came into wide military use during World War II.

I realize that having, or keeping, things "on the radar screen" is a turn of phrase I often use myself. I picked it up when I was a junior editor in the Monitor's international news department, where we would often speak of something being "on the screen," or occasionally, of its having fallen off it.

It was implicitly a radar screen, albeit a metaphorical one. We had computer screens in those days, but they were single-application terminals. They didn't offer a window on the world, as personal computers do today.

It strikes me as a good metaphor for journalists needing to keep scanning their "fields," whether geographic or thematic, for developing trends, controversies brewing, storm clouds gathering, and such.

Another expression conveying a similar sense of a systematic sweep of an area is tour d'horizon. It's French and means literally a tour, or circuit, of the horizon. It's often used to mean a general survey, in a figurative sense, rather than a tour of actual geography. A diplomat departing from a post will give his successor a tour d'horizon of the issues in that particular country, for example.

But something in me wants this phrase to come with real geography attached. I keep imagining a sea captain on the bridge of a ship, swinging an elegant brass spyglass around for a full view of the scene. Or a khaki-clad officer in a jeep, who drives to a hill with a commanding view and trains his binoculars off into the distance.

Trying to get a sense of just how widely used the "radar" trope is, I made a brief, well, tour d'horizon, you might say, of Google News. And I ran across a usage that somehow completed the loop from literal to metaphorical back to literal again.

It came up in an Associated Press article about "a new tool for the long arm of the law," as the headline at philly.com put it. It's a license-plate scanner mounted on police cars. It uses small infrared cameras to pick up data from passing cars (to the dismay of civil libertarians).

The license numbers are matched against databases of stolen cars and people wanted for crimes. When the device makes a match, it sends up an alert, and the officers can make an immediate arrest.

The example given in the story was an unremarkable 1991 "clunker" that turned out to be a stolen car. When David Callister of the Arizona Department of Public Safety drove past it in Phoenix, the plate scanner read its license and made a match. An alert sounded inside his cruiser and on the screen of the vehicle's onboard computer, up popped an image of the license plate of the clunker.

"That car wasn't even on my radar screen," the AP quoted Mr. Callister as saying.

No, officer, it wasn't on your radar screen. But it was on your computer screen.