# Horizon (/docs/charts/horizon)

Horizon answers "what happened across this wide-range series — in a 14-pixel row?" The series is cut into bands and
folded: layer opacity carries magnitude, so extremes stay visible at heights where a sparkline would flatten into noise.

**How to read it** — every band rises from the row's bottom edge, positive or negative; darker means farther from the
baseline, not which direction. Above-baseline values shade in the accent color, below-baseline in the negative color, so
direction is never color-alone even though both fold upward the same way.

```tsx
<Horizon
  data={[2, 5, 9, 14, 22, 31, 26, 18, 12, 24, 38, 45, 41, 30, 19, 11, 6, 3, 8, 16, 27, 35, 29, 20]}
  title="Cluster load"
  width={220}
  height={22}
/>
```

## Install

```tsx
import { Horizon } from "@microcharts/react/horizon";

<Horizon data={cpuLoad} title="Cluster load" />
```

Setup (package + stylesheet): [Quickstart](/docs/quickstart#set-up-with-an-ai-agent) or paste [`/agent-setup.md`](/agent-setup.md) into your agent.


## When to use it

- **Good for** — dense monitoring rows (dozens stacked), wide-range series in tight cells.
- **Avoid for** — first-glance audiences (folding needs a key), or a few rows with room (Sparkline).


## Variants

```tsx
// 3 folds only when the range genuinely spans them
<Horizon data={cpuLoad} folds={3} />
```

```tsx
const latencyMs = [18, 22, 19, 25, 31, 20, 17, 24, 29, 21, 19, 26];

<Horizon data={latencyMs} baseline={20} />
```

```tsx
const cpuLoadWatts = [
  200, 500, 900, 1400, 2200, 3100, 2600, 1800, 1200, 2400, 3800, 4500,
];

<Horizon data={cpuLoadWatts} format={{ maximumFractionDigits: 0 }} locale="de-DE" />
```

`format` also takes `Intl.NumberFormatOptions` — with a `locale`, the accessible summary's range and last-value numbers
follow that locale's own grouping ("4.500" in German, not "4,500"). The interactive readout's per-point values localize
the same way; the folded geometry never changes.

## Edge cases

```tsx
const netFlow = [5, -3, 8, -12, 2, -6, 10];

<Horizon data={netFlow} title="Net flow" />
```

```tsx
<Horizon data={[5, 5, 5, 5, 5]} title="Flat" />
```

Negative values take the negative token and fold from the same bottom edge as positive values (the default
`mode="mirror"`) — both directions get darker as they move away from the baseline, so "denser" always means "farther
from typical," never "which sign." Identical values across the whole row still render as a solid block rather than
vanishing, keeping "flat" visibly distinct from "no data."


## Why this default

Two folds is the default because it needs no training to read approximately; three folds trade learnability for density
and should be reserved for ranges that genuinely span them. The `baseline` is authored, never inferred — a fold origin
is a claim about what "normal" means.

## Accessibility

The accessible name reads the unfolded series — **"Trending up 900%. Range 2 to 45. Last value 20."** — so screen-reader
users get the true values, not the folded geometry. The interactive readout announces unfolded values per point.

The interactive entry follows the shared [interaction contract](/docs/accessibility#one-interaction-contract):
arrow keys rove between units on both axes, `Home` and `End` jump to the ends, and a click, tap, `Enter` or
`Space` selects a unit — pinning its readout so it survives blur, until you select it again or press `Escape`.
On touch, a tap pins and a drag scrubs.

## Props

| Prop | Type | Description |
| --- | --- | --- |
| `data` (required) | `(number \| null)[]` | Series over time. |
| `folds` | `2 \| 3` | Band count — 3 only when the range genuinely spans it. |
| `mode` | `"mirror" \| "offset"` | Mirror flips negatives upward (denser); offset keeps up/down. |
| `baseline` | `number` | Fold origin (e.g. a target level) — authored, never inferred. |
| `animate` | `boolean` | (interactive) Opt-in entrance motion when the chart mounts client-side — add `import "@microcharts/react/motion"` once. Inert on the server, on hydrated server HTML, and under `prefers-reduced-motion`. |

Plus the shared grammar — `data`, `domain`, `color`, `title`, `summary`, `format` — and the layout props (`width`, `height`, `className`, `style`) that every chart accepts. Interactive entries also share `animate` and `live`, and — wherever a chart has more than one navigable unit — `onActive`, `onSelect`, `selectedIndex` and `defaultSelectedIndex`; and — wherever the chart shows a hover value — `readout`. See [the shared grammar](/docs/quickstart#the-shared-grammar).