Questions from the Cockpit: Bright city lights (not)

Cameron, a student pilot from Georgia, writes: I’ve read online in several places that the yellow shapes surrounding cities on the VFR Sectional Chart show the appearance of the various cities’ lights at night but I can’t find any source for that in FAA training materials. Can you tell me if it’s true or not?

You are correct that there’s an absolute dearth of readily available official information on this. There’s nothing to be found on the standard legend of the chart itself. Nothing to be found in the Pilot’s Handbook of Aeronautical Knowledge. Nothing to be found in the Aeronautical Information Manual. Even the Aeronautical Chart Users’ Guide, generally the ultimate authority on all things chart related, only says that, “Yellow tinted areas indicate populated places.”

Nothing about bright city lights.

You’re also correct that there’s no shortage of arm-chair pilots sitting at their computers pontificating authoritatively that the yellow markings lay out the appearance of city lights at night. Of course, the shapes surrounding various cities on the charts aren’t the same, so it isn’t a universal “city symbol.”

Still, if the tint is the nocturnal footprint of a city, why wouldn’t the Chart Guide simply say so?

Hmmm…Color me skeptical.

Because, for one thing, city shapes on aeronautical charts haven’t always been yellow. If you look at any of the strip maps from the early-to-mid 1920s, you’ll see the city “shapes” are dark red.

Now, I know that in the Old West, a point of municipal pride was the size of the community’s red-light district, but I think that was long over by the time men (and women) took to the air. And even if it wasn’t, I’m pretty sure that the red-light district is more of a metaphorical concept than a street lighting plan.

Still, if I’m wrong about that, I’m sure we can all agree that even the largest red-light distinct in history wouldn’t be wide-spread enough to turn an entire city red when viewed from the air. So if the shape of the city on the chart was supposed to be a representation of its night-time footprint, red seems like an odd color choice.

Of course, not only were cities and towns red on 1920s aeronautical charts, so too were airports, beacons, and measures of magnetic declination. Red. Red. And red. Some maps even included a first-generation Chart Supplement with drawings and descriptions of airfields in the margin of the chart, again printed in red.

In fact, there’s so much red ink that sorting out features on the chart makes you see red pretty quickly. Which might be why some other color needed to be broken out for charts in the years that followed, and in 1927, we first see cities going yellow.

Why yellow? I couldn’t find that out, but I’m guessing it was chosen as it wasn’t red (which would continue to be used for aviation-specific content for many years), and it was a color that would contrast with any of the already established terrain altitude shading tints — which are the same general range of colors we use today.

But why separate cities from aviation content? Well, that’s what was happening in the real world at the time. The nature of towns — for fliers — was changing. As aviation matured, the importance of towns for aerial navigation was rapidly diminishing. A town is a key nav aid for contact flying, but as navigational beacons proliferated, and radio ranges were established, the role of cities in navigation began to take a back seat.

In short, cities ceased being primary aerial navigation resources, and didn’t need to be color-coded as such.

Of course, there’s a transition period that follows with some of the charts in 1928 still having red cities but, by 1929, city red only survives in one place: In the printed names of “Air Marked” cities — towns with their names painted on the roof of their largest buildings — whose names were printed on the charts in black ALL CAPS, underlined in red. But their shape outlines are yellow.

Hey, why the red in the first place? Well, most civilian and military maps of the time marked roads and highways in red and some did the same with cities. As the new maps were marking highways in the sky, it probably made sense to just follow convention rather than re-invent the wheel.

Okay, remember at the start of all of this I said that there’s an absolute dearth of readily available official information on the subject? Well, that doesn’t mean the information isn’t out there, you just have to have the patience to dig for it.

I reached out to the FAA to see what they could tell me, and in due course, Rick Breitenfeldt, an FAA Public Affairs Specialist, sent me a copy of some light reading titled, “United States Government Specifications for the Sectional Aeronautical and VFR Terminal Area Charts.” Buried in this book is your answer.

The yellow tint around cities is called the “visual outline” by the map makers, and the manual notes that the outline, “shall reflect the physical shape of a developed area as viewed by the air observer.”

This shape “need not conform to a political boundary nor necessarily represent the extent of building development,” it continues.

We’re told it can include street patterns, buildings, industry, resorts, and even “cemeteries, outlying buildings, parks and gardens, estates, and other features which contribute to the developed area.”

Where does the shape come from? Brietenfeldt tells me that the “FAA Visual Charting Team uses satellite imagery to update ‘city-tint,’ or built up areas, as often as time permits.”

So, basically the yellow tint shows what the city looks like from above. During the day.

It has nothing to do with lights.

So why is it that so many people are teaching that it does? Is it as simple as someone seeing yellow on a map, not finding any readily available explanation, and assuming it symbolizes lights? Or was there a city light map at some time in the past?

I was initially excited to learn that some of the strip maps in the 1930s had a “Night Flying Map” printed on the backside. Ah ha, I thought to myself! At last, the source of the city light myth!

Well, I was excited until I saw some of them, that is. The night maps are largely black and white charts, with terrain virtually non-existent, and all flying features marked in red (airports, beacons, radio ranges). Larger cities have shapes, marked with black hash marks, but they appear no different in shape than the yellow markings on the day side of the charts.

Although there is one kind of map that — at a glance — looks special.

A series of rare hardbound experimental aeronautical charts in the collection of the Connecticut State Library includes several unusual night flying maps, each printed in reverse with white lettering and symbols on a black background.

But these, too, do not mark city lights. In fact, the fine print in the legend tells us that the “base map” is provided by the Automobile Club of Southern California. Right. It’s basically a garden-variety street map with aeronautical features overlaid.

Turn out the lights. The party’s over.

So that’s the answer, Cameron. There is not now, nor does it appear that there ever was, a common aeronautical chart that shows us the pattern of city lights from above. The yellow tint being the outline of city lights at night, sadly, is another piece of CFI mythology.

William E. Dubois is an aviation writer, commercial pilot, and two-time National Champion Air Racer. He loves paper maps, but flies with a glass one — both day and night.