Skylines, played

A skyline and a spectrum analyser are the same picture. So the picture is played.

Both are a row of vertical bars of varying height. That is a coincidence of drawing conventions rather than of physics, but it is usable: if a skyline can be read as a spectrum, it can be played, and the sound will change as the listener turns. This tool does that for twenty-seven cities, using published building heights and coordinates.

Interactive

27 cities

The upper panel is a wheel of the city's towers, up to a hundred and twenty of them, with the far side drawn in a colder colour because it is behind the listener. The lower panel is the same ring as a meter, and the meter is what sounds. Drag to turn, or press Spin.

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What is measured and what is invented

Sonification tends to blur the line between what was observed and what was composed, so it is drawn sharply here.

Measured. Each building carries a published structural height and a published coordinate. The listener stands at a stated point, and each tower's bearing and apparent height follow from those two numbers by trigonometry. Where a tower stands behind a taller one it contributes nothing, which is what an eye does.

Assumed. Footprint width is not recorded anywhere usable, so each tower is given a width of eighteen per cent of its height, between twenty-five and seventy metres. That is about right for a slender tower and about wrong for a broad one.

Rearranged. The spacing around the wheel, and nothing else. Buildings hold their true compass order, clockwise from north; the angle between any two of them does not survive. A downtown occupies perhaps forty degrees of a real horizon, and a wheel that reproduced that would be two-thirds empty. A transit map takes the same liberty with distance, for the same reason.

Invented. The sound. There is no sense in which a city has a pitch. The mapping is a choice, it is written out in full below, and it is deterministic: the same city at the same bearing always makes the same sound.

The key

City	Key	From
New York	Bb blues	Gershwin, Rhapsody in Blue - the opening clarinet glissando arrives on B flat, and the piece was written as a portrait of the city
Dubai	D hijaz	maqam Hijaz, the mode most characteristic of Gulf music
Shenzhen	D pent major	gong mode
Tokyo	D yo	the yo scale, the pentatonic used in Japanese folk and much gagaku-derived music
Chicago	E blues	the Chicago blues, which is a named genre of the city; E is the guitar's home key and the one most of it is played in
Toronto	G major	O Canada, published in G major
Paris	C major	Edith Piaf, La Vie en rose, recorded in C major
Moscow	Eb major	Tchaikovsky, 1812 Overture, op. 49, in E flat major
Taipei	G pent minor	yu mode
Hong Kong	E pent minor	yu mode, as in Cantonese opera
Tel Aviv	D hijaz	Ahava Rabbah, the Jewish liturgical mode with the same interval structure as Hijaz
Seoul	G pent major	the pyeongjo mode of Korean court music, a major pentatonic
Austin	E blues	Stevie Ray Vaughan, whose Texas blues is the city's own sound, played in E on a guitar tuned down a half step
Fort Worth	C major	George Strait, Does Fort Worth Ever Cross Your Mind, recorded in C major
Nashville	G major	the Nashville Number System, the chord notation this city invented and still runs sessions on; G is the key its session players default to

The thirteen with the most skyline, then Fort Worth and Nashville. Nineteen distinct keys across eight modes in all.

How the bars become sound

Ninety-six bars is the right number to look at and the wrong number to play. Four octaves of a five-note scale is twenty pitches, so five or six adjacent bars would land on the same note and become five oscillators detuned by nothing, beating against each other. The bars are mapped onto the distinct pitches of the scale instead, and a pitch takes the loudest bar that feeds it: twenty-odd real partials, ninety-six bars, no unison mud.

Property of the bar	Property of the sound	Why
Position across the view	Pitch, four octaves of the city's scale	A skyline is not a melody, and there is no reason to make an arbitrary arrangement of towers sound like a mistake.
Apparent height	Loudness of that partial, as height to the power 1.6	The exponent makes the peaks stand out in the ear the way they already do in the picture.
Empty horizon	Silence	Which is why turning away from the towers quiets the instrument rather than merely changing it.