Heat Map with Legend

A week, hour by hour: each cell is colored by its value, and the legend below gives the scale. Weekday working hours stand out, while the weekend stays quiet.

  • Try it:
  • Point at a cell: the legend marks its value
Get the code JavaScript JSON
About this chart

When a heat map works

A heat map swaps numbers for colors, so a table of 168 values becomes a pattern you see at once: busy hours, quiet days, the odd spike. It suits two categories that cross, like days and hours, where a line or column chart would need a series for every row.

Good for

  • Website traffic or sales by day and hour
  • Schedules, bookings and occupancy
  • Spotting patterns in a big table

Think twice when

  • Exact values: colors give a rough reading, so add tooltips or labels
  • Readers with color vision deficiency: pick a scale that also changes in lightness
  • A trend over weeks or months: a line chart shows it better
For developers

Get the code.

Built with amCharts 5, a JavaScript library. The JavaScript includes your theme and renderer (canvas or SVG); the JSON also follows the changes you make with the controls.

// Create root element
// https://www.amcharts.com/docs/v5/getting-started/#Root_element
var root = am5.Root.new("chartdiv");

// Set themes
// https://www.amcharts.com/docs/v5/concepts/themes/
root.setThemes([
  am5themes_Animated.new(root),
  am5themes_Responsive.new(root)
]);

// Create chart
// https://www.amcharts.com/docs/v5/charts/xy-chart/
var chart = root.container.children.push(am5xy.XYChart.new(root, {
  panX: false,    // no dragging the plot
  panY: false,
  wheelX: "none", // the mouse wheel scrolls the page, not the chart
  wheelY: "none",
  paddingLeft: 0, // the weekday labels sit at the chart's left edge
  layout: root.verticalLayout
}));

// Create axes and their renderers
var yRenderer = am5xy.AxisRendererY.new(root, {
  visible: false,      // no axis line
  minGridDistance: 20, // at least 20px between labels
  // the first day in the data, Sunday, at the top
  inversed: true,
  minorGridEnabled: true
});

yRenderer.grid.template.set("visible", false); // no grid lines

var yAxis = chart.yAxes.push(am5xy.CategoryAxis.new(root, {
  maxDeviation: 0, // no panning past the first or last day
  renderer: yRenderer,
  categoryField: "weekday"
}));

var xRenderer = am5xy.AxisRendererX.new(root, {
  visible: false, // no axis line
  // every second hour, so the labels don't run into each other
  minGridDistance: 50,
  opposite: true, // the hours along the top
  minorGridEnabled: true
});

xRenderer.grid.template.set("visible", false); // no grid lines

var xAxis = chart.xAxes.push(am5xy.CategoryAxis.new(root, {
  renderer: xRenderer,
  categoryField: "hour"
}));

// Create series
// https://www.amcharts.com/docs/v5/charts/xy-chart/#Adding_series
var series = chart.series.push(am5xy.ColumnSeries.new(root, {
  // works out valueLow and valueHigh, which the heat rules and the legend use
  calculateAggregates: true,
  // gaps between the cells in the chart's background color
  stroke: root.interfaceColors.get("background"),
  clustered: false,   // a cell never shares its space with other series' columns
  xAxis: xAxis,
  yAxis: yAxis,
  categoryXField: "hour",
  categoryYField: "weekday",
  valueField: "value" // the value the heat rules color the cells by
}));

series.columns.template.setAll({
  tooltipText: "{categoryY}, {categoryX}: {value}", // as "Sunday, 12am: 2,990"
  strokeOpacity: 1,        // solid...
  strokeWidth: 2,          // ...2px gaps
  width: am5.percent(100), // each cell fills its hour...
  height: am5.percent(100) // ...and its day
});

// hovering a cell marks its value on the heat legend
series.columns.template.events.on("pointerover", function(event) {
  var di = event.target.dataItem;
  if (di) {
    heatLegend.showValue(di.get("value", 0));
  }
});

// the legend runs from the lowest value on the left to the highest on the right
series.events.on("datavalidated", function() {
  heatLegend.set("startValue", series.getPrivate("valueLow"));
  heatLegend.set("endValue", series.getPrivate("valueHigh"));
});

// Set up heat rules: from the theme's first color for the lowest value to a later one for the highest, so the cells
// follow the theme and dark mode
// https://www.amcharts.com/docs/v5/concepts/settings/heat-rules/
var lowColor = chart.get("colors").getIndex(0);
var highColor = chart.get("colors").getIndex(5);

series.set("heatRules", [{
  target: series.columns.template,
  min: lowColor,
  max: highColor,
  dataField: "value",
  key: "fill"               // the heat rule sets each cell's fill
}]);

// Add heat legend
// https://www.amcharts.com/docs/v5/concepts/legend/heat-legend/
var heatLegend = chart.bottomAxesContainer.children.push(am5.HeatLegend.new(root, {
  orientation: "horizontal",       // a color bar along the bottom
  marginTop: 10,                   // 10px below the plot
  startColor: lowColor,            // the same colors as the heat rule
  endColor: highColor
}));

// Set data
// https://www.amcharts.com/docs/v5/charts/xy-chart/#Setting_data
var data = [{
  hour: "12am",
  weekday: "Sunday",
  value: 2990
}, {
  hour: "1am",
  weekday: "Sunday",
  value: 2520
}, {
  hour: "2am",
  weekday: "Sunday",
  value: 2334
}, {
  hour: "3am",
  weekday: "Sunday",
  value: 2230
}, {
  hour: "4am",
  weekday: "Sunday",
  value: 2325
}, {
  hour: "5am",
  weekday: "Sunday",
  value: 2019
}, {
  hour: "6am",
  weekday: "Sunday",
  value: 2128
}, {
  hour: "7am",
  weekday: "Sunday",
  value: 2246
}, {
  hour: "8am",
  weekday: "Sunday",
  value: 2421
}, {
  hour: "9am",
  weekday: "Sunday",
  value: 2788
}, {
  hour: "10am",
  weekday: "Sunday",
  value: 2959
}, {
  hour: "11am",
  weekday: "Sunday",
  value: 3018
}, {
  hour: "12pm",
  weekday: "Sunday",
  value: 3154
}, {
  hour: "1pm",
  weekday: "Sunday",
  value: 3172
}, {
  hour: "2pm",
  weekday: "Sunday",
  value: 3368
}, {
  hour: "3pm",
  weekday: "Sunday",
  value: 3464
}, {
  hour: "4pm",
  weekday: "Sunday",
  value: 3746
}, {
  hour: "5pm",
  weekday: "Sunday",
  value: 3656
}, {
  hour: "6pm",
  weekday: "Sunday",
  value: 3336
}, {
  hour: "7pm",
  weekday: "Sunday",
  value: 3292
}, {
  hour: "8pm",
  weekday: "Sunday",
  value: 3269
}, {
  hour: "9pm",
  weekday: "Sunday",
  value: 3300
}, {
  hour: "10pm",
  weekday: "Sunday",
  value: 3403
}, {
  hour: "11pm",
  weekday: "Sunday",
  value: 3323
}, {
  hour: "12am",
  weekday: "Monday",
  value: 3346
}, {
  hour: "1am",
  weekday: "Monday",
  value: 2725
}, {
  hour: "2am",
  weekday: "Monday",
  value: 3052
}, {
  hour: "3am",
  weekday: "Monday",
  value: 3876
}, {
  hour: "4am",
  weekday: "Monday",
  value: 4453
}, {
  hour: "5am",
  weekday: "Monday",
  value: 3972
}, {
  hour: "6am",
  weekday: "Monday",
  value: 4644
}, {
  hour: "7am",
  weekday: "Monday",
  value: 5715
}, {
  hour: "8am",
  weekday: "Monday",
  value: 7080
}, {
  hour: "9am",
  weekday: "Monday",
  value: 8022
}, {
  hour: "10am",
  weekday: "Monday",
  value: 8446
}, {
  hour: "11am",
  weekday: "Monday",
  value: 9313
}, {
  hour: "12pm",
  weekday: "Monday",
  value: 9011
}, {
  hour: "1pm",
  weekday: "Monday",
  value: 8508
}, {
  hour: "2pm",
  weekday: "Monday",
  value: 8515
}, {
  hour: "3pm",
  weekday: "Monday",
  value: 8399
}, {
  hour: "4pm",
  weekday: "Monday",
  value: 8649
}, {
  hour: "5pm",
  weekday: "Monday",
  value: 7869
}, {
  hour: "6pm",
  weekday: "Monday",
  value: 6933
}, {
  hour: "7pm",
  weekday: "Monday",
  value: 5969
}, {
  hour: "8pm",
  weekday: "Monday",
  value: 5552
}, {
  hour: "9pm",
  weekday: "Monday",
  value: 5434
}, {
  hour: "10pm",
  weekday: "Monday",
  value: 5070
}, {
  hour: "11pm",
  weekday: "Monday",
  value: 4851
}, {
  hour: "12am",
  weekday: "Tuesday",
  value: 4468
}, {
  hour: "1am",
  weekday: "Tuesday",
  value: 3306
}, {
  hour: "2am",
  weekday: "Tuesday",
  value: 3906
}, {
  hour: "3am",
  weekday: "Tuesday",
  value: 4413
}, {
  hour: "4am",
  weekday: "Tuesday",
  value: 4726
}, {
  hour: "5am",
  weekday: "Tuesday",
  value: 4584
}, {
  hour: "6am",
  weekday: "Tuesday",
  value: 5717
}, {
  hour: "7am",
  weekday: "Tuesday",
  value: 6504
}, {
  hour: "8am",
  weekday: "Tuesday",
  value: 8104
}, {
  hour: "9am",
  weekday: "Tuesday",
  value: 8813
}, {
  hour: "10am",
  weekday: "Tuesday",
  value: 9278
}, {
  hour: "11am",
  weekday: "Tuesday",
  value: 10425
}, {
  hour: "12pm",
  weekday: "Tuesday",
  value: 10137
}, {
  hour: "1pm",
  weekday: "Tuesday",
  value: 9290
}, {
  hour: "2pm",
  weekday: "Tuesday",
  value: 9255
}, {
  hour: "3pm",
  weekday: "Tuesday",
  value: 9614
}, {
  hour: "4pm",
  weekday: "Tuesday",
  value: 9713
}, {
  hour: "5pm",
  weekday: "Tuesday",
  value: 9667
}, {
  hour: "6pm",
  weekday: "Tuesday",
  value: 8774
}, {
  hour: "7pm",
  weekday: "Tuesday",
  value: 8649
}, {
  hour: "8pm",
  weekday: "Tuesday",
  value: 9937
}, {
  hour: "9pm",
  weekday: "Tuesday",
  value: 10286
}, {
  hour: "10pm",
  weekday: "Tuesday",
  value: 9175
}, {
  hour: "11pm",
  weekday: "Tuesday",
  value: 8581
}, {
  hour: "12am",
  weekday: "Wednesday",
  value: 8145
}, {
  hour: "1am",
  weekday: "Wednesday",
  value: 7177
}, {
  hour: "2am",
  weekday: "Wednesday",
  value: 5657
}, {
  hour: "3am",
  weekday: "Wednesday",
  value: 6802
}, {
  hour: "4am",
  weekday: "Wednesday",
  value: 8159
}, {
  hour: "5am",
  weekday: "Wednesday",
  value: 8449
}, {
  hour: "6am",
  weekday: "Wednesday",
  value: 9453
}, {
  hour: "7am",
  weekday: "Wednesday",
  value: 9947
}, {
  hour: "8am",
  weekday: "Wednesday",
  value: 11471
}, {
  hour: "9am",
  weekday: "Wednesday",
  value: 12492
}, {
  hour: "10am",
  weekday: "Wednesday",
  value: 9388
}, {
  hour: "11am",
  weekday: "Wednesday",
  value: 9928
}, {
  hour: "12pm",
  weekday: "Wednesday",
  value: 9644
}, {
  hour: "1pm",
  weekday: "Wednesday",
  value: 9034
}, {
  hour: "2pm",
  weekday: "Wednesday",
  value: 8964
}, {
  hour: "3pm",
  weekday: "Wednesday",
  value: 9069
}, {
  hour: "4pm",
  weekday: "Wednesday",
  value: 8898
}, {
  hour: "5pm",
  weekday: "Wednesday",
  value: 8322
}, {
  hour: "6pm",
  weekday: "Wednesday",
  value: 6909
}, {
  hour: "7pm",
  weekday: "Wednesday",
  value: 5810
}, {
  hour: "8pm",
  weekday: "Wednesday",
  value: 5151
}, {
  hour: "9pm",
  weekday: "Wednesday",
  value: 4911
}, {
  hour: "10pm",
  weekday: "Wednesday",
  value: 4487
}, {
  hour: "11pm",
  weekday: "Wednesday",
  value: 4118
}, {
  hour: "12am",
  weekday: "Thursday",
  value: 3689
}, {
  hour: "1am",
  weekday: "Thursday",
  value: 3081
}, {
  hour: "2am",
  weekday: "Thursday",
  value: 6525
}, {
  hour: "3am",
  weekday: "Thursday",
  value: 6228
}, {
  hour: "4am",
  weekday: "Thursday",
  value: 6917
}, {
  hour: "5am",
  weekday: "Thursday",
  value: 6568
}, {
  hour: "6am",
  weekday: "Thursday",
  value: 6405
}, {
  hour: "7am",
  weekday: "Thursday",
  value: 8106
}, {
  hour: "8am",
  weekday: "Thursday",
  value: 8542
}, {
  hour: "9am",
  weekday: "Thursday",
  value: 8501
}, {
  hour: "10am",
  weekday: "Thursday",
  value: 8802
}, {
  hour: "11am",
  weekday: "Thursday",
  value: 9420
}, {
  hour: "12pm",
  weekday: "Thursday",
  value: 8966
}, {
  hour: "1pm",
  weekday: "Thursday",
  value: 8135
}, {
  hour: "2pm",
  weekday: "Thursday",
  value: 8224
}, {
  hour: "3pm",
  weekday: "Thursday",
  value: 8387
}, {
  hour: "4pm",
  weekday: "Thursday",
  value: 8218
}, {
  hour: "5pm",
  weekday: "Thursday",
  value: 7641
}, {
  hour: "6pm",
  weekday: "Thursday",
  value: 6469
}, {
  hour: "7pm",
  weekday: "Thursday",
  value: 5441
}, {
  hour: "8pm",
  weekday: "Thursday",
  value: 4952
}, {
  hour: "9pm",
  weekday: "Thursday",
  value: 4643
}, {
  hour: "10pm",
  weekday: "Thursday",
  value: 4393
}, {
  hour: "11pm",
  weekday: "Thursday",
  value: 4017
}, {
  hour: "12am",
  weekday: "Friday",
  value: 4022
}, {
  hour: "1am",
  weekday: "Friday",
  value: 3063
}, {
  hour: "2am",
  weekday: "Friday",
  value: 3638
}, {
  hour: "3am",
  weekday: "Friday",
  value: 3968
}, {
  hour: "4am",
  weekday: "Friday",
  value: 4070
}, {
  hour: "5am",
  weekday: "Friday",
  value: 4019
}, {
  hour: "6am",
  weekday: "Friday",
  value: 4548
}, {
  hour: "7am",
  weekday: "Friday",
  value: 5465
}, {
  hour: "8am",
  weekday: "Friday",
  value: 6909
}, {
  hour: "9am",
  weekday: "Friday",
  value: 7706
}, {
  hour: "10am",
  weekday: "Friday",
  value: 7867
}, {
  hour: "11am",
  weekday: "Friday",
  value: 8615
}, {
  hour: "12pm",
  weekday: "Friday",
  value: 8218
}, {
  hour: "1pm",
  weekday: "Friday",
  value: 7604
}, {
  hour: "2pm",
  weekday: "Friday",
  value: 7429
}, {
  hour: "3pm",
  weekday: "Friday",
  value: 7488
}, {
  hour: "4pm",
  weekday: "Friday",
  value: 7493
}, {
  hour: "5pm",
  weekday: "Friday",
  value: 6998
}, {
  hour: "6pm",
  weekday: "Friday",
  value: 5941
}, {
  hour: "7pm",
  weekday: "Friday",
  value: 5068
}, {
  hour: "8pm",
  weekday: "Friday",
  value: 4636
}, {
  hour: "9pm",
  weekday: "Friday",
  value: 4241
}, {
  hour: "10pm",
  weekday: "Friday",
  value: 3858
}, {
  hour: "11pm",
  weekday: "Friday",
  value: 3833
}, {
  hour: "12am",
  weekday: "Saturday",
  value: 3503
}, {
  hour: "1am",
  weekday: "Saturday",
  value: 2842
}, {
  hour: "2am",
  weekday: "Saturday",
  value: 2808
}, {
  hour: "3am",
  weekday: "Saturday",
  value: 2399
}, {
  hour: "4am",
  weekday: "Saturday",
  value: 2280
}, {
  hour: "5am",
  weekday: "Saturday",
  value: 2139
}, {
  hour: "6am",
  weekday: "Saturday",
  value: 2527
}, {
  hour: "7am",
  weekday: "Saturday",
  value: 2940
}, {
  hour: "8am",
  weekday: "Saturday",
  value: 3066
}, {
  hour: "9am",
  weekday: "Saturday",
  value: 3494
}, {
  hour: "10am",
  weekday: "Saturday",
  value: 3287
}, {
  hour: "11am",
  weekday: "Saturday",
  value: 3416
}, {
  hour: "12pm",
  weekday: "Saturday",
  value: 3432
}, {
  hour: "1pm",
  weekday: "Saturday",
  value: 3523
}, {
  hour: "2pm",
  weekday: "Saturday",
  value: 3542
}, {
  hour: "3pm",
  weekday: "Saturday",
  value: 3347
}, {
  hour: "4pm",
  weekday: "Saturday",
  value: 3292
}, {
  hour: "5pm",
  weekday: "Saturday",
  value: 3416
}, {
  hour: "6pm",
  weekday: "Saturday",
  value: 3131
}, {
  hour: "7pm",
  weekday: "Saturday",
  value: 3057
}, {
  hour: "8pm",
  weekday: "Saturday",
  value: 3227
}, {
  hour: "9pm",
  weekday: "Saturday",
  value: 3060
}, {
  hour: "10pm",
  weekday: "Saturday",
  value: 2855
}, {
  hour: "11pm",
  weekday: "Saturday",
  value: 2625
}
]

series.data.setAll(data);

// Auto-populate X and Y axis category data
var weekdays = [];
var hours = [];
am5.array.each(data, function(row) {
  if (weekdays.indexOf(row.weekday) == -1) {
    weekdays.push(row.weekday);
  }
  if (hours.indexOf(row.hour) == -1) {
    hours.push(row.hour);
  }
});

yAxis.data.setAll(weekdays.map(function(item) {
  return { weekday: item }
}));

xAxis.data.setAll(hours.map(function(item) {
  return { hour: item }
}));

// Make stuff animate on load
// https://www.amcharts.com/docs/v5/concepts/animations/#Initial_animation
chart.appear(1000, 100);

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