I was asked to show everything from the edge of the observable universe to the Planck length as one continuous scale ladder. The condition: not just a table listing orders of magnitude, but accurate positions and proportions as well. The first round produced a 26-step version, and after looking it over, it was at the level of "well made, but." In the end it led to a second round that rebuilt the coordinate system from scratch.
Three things bothered me about the first version
Lack of detail aside, it first needed checking against the real scale. The solar system in particular was short on detail, and the flow of shrinking away from Earth into the next step didn't feel natural; you could see where it had been forced together. The stretch narrowing from a person down to a cell is where any awkwardness in surface, angle or line of sight shows immediately, so I was told to take special care there. Finally came the condition that zooming in and out with the mouse should move on one consistent log/exponential scale, with the size readout on screen exactly right to match. "Let's finish it for real this time," I was told, and as promised it became a rework starting with the coordinate system.
The zoom axis became a true log scale
The first version used a fake axis that squeezed the gap between steps into 1.2 to 3.2 orders of magnitude. The second version defines the axis itself as L = log10(screen width [m]), and computes each step's size directly as scale = W · 10^(log10(typical size) − L). No compression, no correction. One notch of the wheel moves exactly the same number of orders of magnitude anywhere on screen, and the size gauge on screen matches the proportion of the actual screen width. From the observable universe (about 93 billion light-years) to the Planck length (1.616×10⁻³⁵ m), a total of 61.7 orders of magnitude, split into 46 steps. The largest gap between steps is 3.0 orders of magnitude, and one screen spans 4.2, so there's no stretch where the screen goes completely empty.
From Earth to the cell, strung on a single anchor
The reason the transitions felt forced was that every step had its own origin. So I fixed one point, "the back of the hand of a person standing in the middle of Gwanghwamun Square, 0.9 m above the ground," and made every step from Earth to the cell share that point as its origin. In the Earth step, the sphere is rotated so Seoul faces the zenith (+Y), then the whole sphere is pushed out by its radius so the surface sits exactly at the origin. East Asia, the Korean Peninsula and the Seoul metro area aren't flat; they're spherical patches curved to Earth's actual radius (6,371 km), so the curvature carries on unbroken as you zoom in. From Seoul (30 km screen width) on, the edge drops by only about 18 m, so it switches to a flat plane.
The camera elevation angle is also set per step and interpolated. It rises from Earth 20° → East Asia 30° → Seoul 46° → Gwanghwamun Square 50° → people in the square 66° → a person 76° (nearly eye level), then looks down again at the hand, 52°, and continues to the cell at 72°. These values make the view tilt naturally from a bird's-eye view to eye level and back to looking down as things shrink. Stretches that show the same subject repeatedly at different resolutions (3 solar system steps, 12 steps from the ground to the hand) are grouped as mutually exclusive and swap at the midpoint. Otherwise there was a ghosting effect, with the terrain showing up in two overlapping layers.
The solar system cheats, honestly
All nine bodies have their real orbital elements (semi-major axis, eccentricity, inclination, longitude of the ascending node, longitude of perihelion). So Pluto's orbit tilts 17°, squashed, cutting inside Neptune's, and Saturn's rings are drawn at their real extent, 74,500 to 140,180 km. Sizes are all true to scale too, but at a screen width of 60 AU, the Sun's diameter comes out to just 0.2 pixels. Left as is, you'd see nothing. So screen-fixed dot markers are laid over them, and as you zoom in, the true-scale disk pushes the marker aside and shows itself. Rather than exaggerate sizes, the representation uses the fact that from a long way off, planets really do look like point sources. The whole system is shifted so Earth sits at the origin, so when you enter the Earth's orbit step, you can see the Sun off to one side.
I checked the numbers one by one
Once everything was built, I checked by calculation, not by eye. Earth's radius divided by the Earth step's screen width should come out to exactly 0.50000, and it did. The distance to the Moon is 30.2 Earth diameters, the ratio of nucleus to atom size is 1/25,926, the outer radius of the Oort cloud is 1.59 light-years, the Milky Way is 100,400 light-years across, and the observable universe is 93 billion light-years across. Every on-screen size was computed from these values.
Round three: Earth down to the palm, redrawn from measured data
With the second version up on screen, the stretch from Earth to the hand was still weak. The Korean Peninsula looked like an island cut off from the continent, Seoul was cone-shaped mountains and scattered boxes, and the buildings around the square were just big gray pillars. The people stood like mannequins, and the tubes meant to be tendons and veins on the back of the hand looked like hair. On phones, the descriptions covered the scene, and the descriptions only gave scale numbers, nothing about how big that actually is. The third round fixed this list item by item.
The reason the peninsula looked like an island wasn't the shape of the coastline. I'd built the terrain by lowering the height the farther you got from a mountain ridge, so the plains along the west coast and the low ground toward the Yalu and Tumen rivers ended up almost at sea level, and the semi-transparent sea surface covered them. Only the mountains rose above the water, so it looked like an island. Instead of faking terrain with noise, I put in real data. Earth uses NASA Blue Marble (July 2004) satellite imagery; East Asia, the Korean Peninsula and the Seoul metro area use high-resolution tiles of the same imagery draped over measured elevations from Mapzen Terrain Tiles, and the coastline is drawn from Natural Earth 1:10m data. Left at true height, the mountains are nearly invisible, so they're exaggerated 14× for East Asia, 8× for the peninsula, 3× for the metro area and 1.6× for Seoul, and each step's description states the factor.
Seoul, Jongno and Gwanghwamun Square were built from OpenStreetMap data. The Han River, green space and arterial roads are drawn as ground imagery, and 13,507 buildings around Jongno stand on their real footprints. Only about 1,300 of them have a recorded height or floor count, so for the rest the floor count is guessed from floor area and distance from downtown. Buildings that stand out from the square, like the Kyobo Life Building, Government Complex Seoul and the Sejong Center for the Performing Arts, got their real heights entered separately. Gwanghwamun gate and its royal terrace, Geunjeongjeon Hall, and the statues of King Sejong and Admiral Yi Sun-sin were modeled by hand and placed at the coordinates recorded in OSM. The anchor's original coordinates (37.566° N) were actually over by Seoul Plaza, so I moved it to the middle of the square between the two statues (37.5720°, 126.9766°).
The people became models with a walking stride and arm swing, and groups walking were mixed with groups standing face to face, placed so they don't overlap. There was also a problem where, at the hand step, the body vanished and the hand floated in midair. The person scene was fading out first, so the hand step now keeps the same person and is a scene where only the left hand is built in fine detail. The fingers were reposed in a relaxed position, each joint slightly bent. Every step got one comparison sentence, like "Shrink Earth to a basketball and the Moon is a tennis ball 7.2 m away."
How to use it: a log ruler instead of a scroll
Drag to rotate, and use the wheel or a pinch to zoom in and out. The axis moves at a constant log rate, so it feels the same speed wherever you are. ↑↓ skip one step at a time, and you can click the vertical scale (the ruler) on the right to jump straight to the size you want. Press space to start an automatic journey of about 150 seconds, and L to toggle labels. On phones, the descriptions go into a sheet at the bottom, and on-screen buttons handle step navigation, the automatic journey and labels. The satellite imagery, terrain and building footprints are all packed into one HTML file, so it's about 5 MB, and the first time it opens, building the terrain and buildings takes a few seconds.
This version, and the others
This version was made with Claude Opus 5. The same scale ladder also exists as SCALE ASTRA, made with GPT Astra; Scale Gemini 3.6 and Scale Gemini 3.8, made with Gemini; and Scale Odyssey Opus 5.5, rebuilt with Claude Opus 5.5 on real satellite imagery and building data. It's fun to put them side by side and see how each AI solves the same problem differently.