# Line chart in a table

> Show the trend of a measure over time as a line chart in each table row.

A line chart shows how a measure changes over time. This template draws one in every row of a table. For example, for each product, it shows the number of orders per month.

:::info Set up first
Add the function library and import it into your dataset first. See [SVG charts in tables](./index.md).
:::

## Add the metric

Call `SVG.Viz.Line` from a metric of type `text`, and wrap it in `SVG.Html.Box` to fix the size in the cell.

```aml
metric orders_trend {
  label: 'Orders Trend'
  type: 'text'
  definition: @aql
    SVG.Html.Box(
      200, 60,
      SVG.Viz.Line(
        orders,
        orders.created_at | month(),
        count(orders.id),
        null,
        200,
        60
      )
    )
  ;;
}
```

## Parameters

### `SVG.Viz.Line`

`SVG.Viz.Line` takes these parameters in order.

| Parameter | Type | What it is |
|---|---|---|
| `pAxisModel` | `model` | The model the time dimension belongs to, such as `orders`. |
| `pAxisRef` | `dimension` | A date or datetime dimension, one point per value, such as `orders.created_at \| month()`. |
| `pMeasureRef` | `number` | The measure to plot, such as `count(orders.id)`. |
| `pColor` | `text` | Line color. `null` uses `#01B8AA`. |
| `pWidth` | `number` | Width of the chart's drawing grid. Sets the proportions, not the display size. `null` uses 120. |
| `pHeight` | `number` | Height of the chart's drawing grid. Sets the proportions, not the display size. `null` uses 48. |

### `SVG.Html.Box`

`SVG.Html.Box` sets how big the chart looks in the table cell. Without it, the chart stretches to the full width of the cell.

| Parameter | Type | What it is |
|---|---|---|
| `pWidth` | `number` | Display width in pixels. |
| `pHeight` | `number` | Display height in pixels. |
| `pContents` | `text` | The chart to show, such as the result of `SVG.Viz.Line`. |

The chart scales to fit this box and keeps its proportions. Use the same width-to-height ratio as the chart's `pWidth` and `pHeight`, or the chart leaves empty space around it.

## Use it in a table

Put the metric next to the dimension you want a row for. Don't add the time dimension to the table: the chart draws the periods inside each cell.

```aql
explore {
  dimensions {
    product_name: products.name
  }
  measures {
    orders_trend: orders_trend
  }
}
```

## How to read it

- Each point is one period of `pAxisRef`, from left to right in time order. Points are spaced by date, so a gap in the data shows as a longer segment.
- Periods with no value are skipped.
- The vertical scale starts at 0, or at the lowest value if it is negative, and ends at the highest value of the row.
- Each row has its own scale, so compare the shape of the lines, not their height.
- A row with only one period shows a single dot.