How a plate is computed
You cannot tell, by looking at it, whether a map was computed or traced. Both arrive as a picture of a coastline.
So this page is the manufacturing rather than the merit: what the data is, how the frame gets decided, and what happens between your settings and the file. Six steps. No claim on this page is about how good the result is.
The order becomes coordinates and an instant
Everything you set on the card is resolved to numbers before a single line is drawn: a longitude and a latitude, a moment on the clock in the zone that moment belongs to, and the proportion of the sheet. The words you chose from — the name of a country, the name of an ink — do not travel any further than that first step.
This is why the settings can live in the address bar. The design is not a file we picked out for you; it is a short list of numbers, and the same list always produces the same sheet.
The sky is solved for that instant
The sun, the moon and the planets are computed for your moment and your horizon from JPL's DE441 ephemeris — the same solar-system solution used for mission planning. The fixed stars come from a catalogue, each one carrying its own recorded position, magnitude and colour.
Nothing is read off a table of rounded dates, and there is no nearest-of-eight moon icon anywhere in this shop. Change the minute and the drawing changes: the phase is a real terminator falling across real terrain, and the sky over midnight is not the sky over ten o'clock.
The ground is read from published survey
Coastlines, rivers, lakes, national borders and the time-zone lines are drawn from public survey data. Height and depth come from the ETOPO1 and GEBCO grids — the same soundings and satellite altimetry the hydrographic offices publish, so a relief sheet is a calculation over a field of measured elevations rather than a painting of one. Cities come from a gazetteer that carries a population against every name.
Nothing on any sheet is traced from somebody else's map and nothing is scanned. There is no library of pre-drawn artwork behind this shop, which is also why there is no design here that we cannot draw at a different size, in a different palette, around a different place.
The frame is computed from your sheet, not cut out of a poster
The window is the smallest one of your sheet's proportion that still contains the place, centred on it and clamped at the poles. Portrait and landscape are therefore two drawings rather than one drawing cropped twice — ask for Spain tall and you get Spain tall, with the frame worked out for that shape, not a letterbox with the ends chopped off.
Where a combination is geometrically impossible the control is greyed rather than quietly faked. A sheet of the whole world cannot be made portrait: longitude runs the whole way round and latitude stops at the poles, so the proportion you asked for does not exist on a globe. You are told that, and told why, instead of being handed a squashed world.
It is drawn oversize, then brought down
Every plate is rendered larger than it will be shown and reduced afterwards, so a hairline river lands as a hairline instead of as a staircase, and a coastline keeps its small bays at small sizes.
The labelling is decided in the same pass. A population figure sets which names print; capitals are kept whatever their size; and the dots are given the same threshold as the names, so that what is marked and what is named agree. A map whose dots and labels disagree reads as speckle, and that is a manufacturing defect rather than a style.
The file is made at the moment you ask, and not kept
No plate exists before you ask for it. The sheet is drawn from your numbers when you request it, in the palette you picked, and the palette is applied last — the drawing underneath is identical whichever ink you choose, which is why you can change your mind about the colour without changing the map.
Several of the sheets paint inside your own browser: a few kilobytes of numbers arrive, the drawing happens on your machine, and the file is written there. Where a sheet is drawn on our side instead, the parameters are used for that drawing and discarded. We keep no library of what anybody asked for, which means we also cannot hand you back a copy — if you want the same sheet again, you ask for it again, and it is drawn again.
What is under the drawing
The inputs, named. Every one of them is published by somebody other than us and can be checked against what arrives.
- The sun, moon and planets
- JPL's DE441 ephemeris, evaluated for your instant and your horizon
- The stars
- Two and a half million catalogued stars, each at its recorded position, magnitude and colour
- The moon's surface
- NASA's lunar albedo map, turned to the libration angle computed for your instant
- Height and depth
- The ETOPO1 and GEBCO grids — public soundings and satellite altimetry
- Coast, river, lake, border, time zone
- Published survey data, attributable line by line
- Cities
- A gazetteer carrying a population and a rank against every name
- Sheet proportions
- 2:1 landscape and 4:5 portrait, each drawn for its own frame
- Palettes
- Five house inks — four for dark grounds, one drawn for printing on white stock
- What you receive
- A print-ready file. Sheet sizes announced at launch.
What this does not do
The same specification, from the other side.
- It is not a horoscope
- There is no astrology anywhere in this shop, in any product, at any setting. The sky here is the sky an observatory would describe.
- It cannot see the weather
- A sheet knows where everything was. It has nothing to say about whether the cloud let you see it.
- It will not invent a border
- A border is a claim rather than a measurement. We draw the survey we have and do not adjudicate the ones in dispute.
- It does not round to look tidy
- Times are solved and then rounded only to what a page can usefully print. Where a figure is genuinely uncertain, the width of the uncertainty is printed with it.
Ask for the same sheet in ten years and it will be drawn again — from the same published data, by the same rules, out of the same short list of numbers. It will not be fetched out of a folder of finished pictures, because there is no folder.
Kairoi Co. OÜ — Sakala tn 7-2, Tallinn, Estonia. Reg. No. 17410529.