The sky

The sky is the product. Everything else — the server, the imports, the pipelines — exists to put it on screen.

Stars are artists

Every artist in the universe is a star. Brightness is popularity, so the map has an immediate visual hierarchy: the names everyone knows are the ones that carry across a zoomed-out view, and the long tail is there but faint.

Position is not decorative. Artists that are listened to together sit near each other, because the layout is a projection of a similarity graph. Distance on the map means something, which is what makes travelling across it worth doing.

Nebulae are genres

Genres are not labels pinned to stars; they are regions. A nebula is drawn from the density of a genre in an area, so scenes appear as glowing clouds with real shapes — overlapping where genres overlap, sharp where they do not.

The layout is canonical

One layout, computed offline and versioned, shared by everyone. This is a deliberate constraint:

• A coordinate is a place. You can link to it, screenshot it, and describe it to someone else — and they will see the same thing.
• Landmarks are shared. “Between the two big post-punk clusters” is a direction, not a private impression.
• Re-laying the map silently would move everyone’s landmarks, so the canon is versioned rather than continuously recomputed.

How the coordinates are actually computed — and why the layout is written here rather than taken from a library — is in Building the sky and ADR 0008. What the client receives is in the tile format.

The address is the view

Because the map is the same for everyone, the URL can carry a place:

/star/54#-59.17,-69.55,12
 └ which card is open   └ where the camera is

The two halves behave differently on purpose. The path is what a link is about — “look at this artist” — so it is a real route the server answers, and it is what a chat preview or a crawler reads. The fragment is the camera, and a fragment is never sent to the server: it is a client-side bookmark, which is exactly what a camera position is. It also changes on every pan and zoom, and putting that in the path would fill the session history with entries nobody wants to press Back through — so the address is replaced rather than pushed.

A link to a star with no fragment flies to it. A link with one honours the fragment instead, because it says where the sender was looking — which may be a wide view holding that star among others. A fragment that has been truncated or hand-edited opens the whole sky rather than a camera at nowhere.

The star whose card is open wears a halo, because arriving somewhere is no use if you cannot tell which point of light you arrived at. It is drawn as a second pass over the field rather than as a property of every star — the field is one instanced draw call whose cost is measured, and a per-star comparison would spend that budget on two hundred thousand stars to change one. Its size is in pixels, not world units, so it stays a marker at every zoom rather than becoming an object that grows as you approach.

The other way to take a view with you is a poster: the frame as drawn, saved as a PNG at the resolution it is drawn. It is captured inside the render loop — a WebGL colour buffer is undefined the moment a frame ends, so a screenshot taken from outside would save an empty image.

The fog is yours

The only per-user layer of the map is the fog of war: what you have and have not heard. It is a small coverage texture, kilobytes in size, sampled while stars are drawn.

In exploration mode the fog starts closed and lifts as you listen. In creative mode the sky is open from the first minute — the fog is still recorded, but as a record of your listening rather than a gate on it.

Why it renders the way it does

The sky is a map, not a game world: a huge static universe browsed with a camera. That shape decides the architecture — a tile pyramid served as static files, and a thin custom WebGL2 renderer that draws every visible star in one instanced draw call. The reasoning is recorded in ADR 0003.