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What do people call a chart like one below which has days on Y axis and time of the day on X axis while color represents the level of some value (for example, loading, usage count, etc.)?

The chart looks like: enter image description here

If I want to ask on forums how to implement one with the specific tool what is the best way to name it additionally to the image and description?

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  • $\begingroup$ What happens if values are exactly 15, 30, 45? Perhaps that doesn't bite. $\endgroup$
    – Nick Cox
    Commented May 24 at 12:47
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    $\begingroup$ Maybe a kind of heat map? $\endgroup$ Commented May 24 at 20:34
  • $\begingroup$ I gave the longest answer to date. Given the question If I want to ask on forums how to implement one with the specific tool what is the best way to name it additionally to the image and description? the shortest answer to date is that if you give a clear description and image, then the name really doesn't matter much: indeed it may mislead some readers. How would you do this in particular software? is a fair question for any forum centred on such software. $\endgroup$
    – Nick Cox
    Commented May 26 at 10:50
  • $\begingroup$ @NickCox, absolutely. The only point is the "Title" string for the question. I guess that if instead of "How to implement this kind of a chart" it will have more specific name like "How to implement bar-style heat map for week loading?" it would help both to catch people how could know the answer (some ready stuff) as well as to others who will later search for this solution on the forums. It is hard to search for "this kind of a chart" and much easier and more productive to search for something more specific. And I agree that wrong name could be counter productive here, of course. $\endgroup$ Commented May 26 at 11:47
  • $\begingroup$ The issue is epitomised (if trivially) by your accepting an answer that says it's a kind of heat map. I am fine with you accepting whatever is most helpful, but I wouldn't call the plot a heat map at all -- yet I can see why people say that. Hence my long answer, in effect that we need names, but they often mislead. I am happy if anyone thinks that is too obvious to underline. $\endgroup$
    – Nick Cox
    Commented May 26 at 11:53

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This looks like a kind of heatmap to me. Often heatmaps will have unordered categories and they will be clustered with the clusterings displayed in the margins, but you don't have to have that (and you don't here).

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  • $\begingroup$ Thank you so much (will accept tomorrow as recommended by SE). I somehow missed this mostly because I was focused on another usage of the map. Namely, my case is when I have different colors for different activities (like green for coding, blue for code reviews, red for testing, etc.) and I want to show these activities on the map. Different situation and different name should be. My bad in wording here. Do you have any ideas what this kind of map could be or it would be better if I rise another question? $\endgroup$ Commented May 24 at 11:46
  • $\begingroup$ @DamirTenishev, I don't know what / if there's a special name for the other kind you describe. In terms of getting software to make one, you should be able to shoehorn a regular heatmap function easily enough (give each cell a different number based on the activity, make the heatmap, & change the legend). $\endgroup$ Commented May 24 at 11:50
  • $\begingroup$ Thank you. Seems it would be better to raise a separate question for this to avoid mess here with my initial wording. Anyway, thank you again, the answer with the heat map helped with the direction. $\endgroup$ Commented May 24 at 12:08
  • $\begingroup$ Don't mix red and green! $\endgroup$
    – Nick Cox
    Commented May 24 at 12:45
  • $\begingroup$ Just as a second thought. I really missed that this is just a heatmap, so thank you for the answer. But along with that my focus was on the particular time-ranged structure of the diagram, when both axes have time, but X has repeating time of a day and Y axis has (possibly repeated) day of a week. So, the second part of the question was if the "every point representation" is a heat map, how could I specify this "dual-time" nature of the chart. So far, "bar chart" the best generalization, but it doesn't specify these features. $\endgroup$ Commented May 25 at 11:34
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A data visualization technique of using color or intensity to represent a numeric value is usually called a "heatmap". A data visualization technique that shows intensities over time on an x-axis, and replicates such as the days of the week shown on the y-axis (or vice versa), I have seen called a raster plot.

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  • $\begingroup$ Thank you. Just to make you notice the comment the same question I have to @gung-Reinstate Monica. I really missed that this is just a heatmap, so thank you. But along with that my focus was on the particular time-ranged structure of the diagram, when both axes have time, but X has repeating time of a day and Y axis has (possibly repeated) day of a week. So, the second part of the question was if the "every point representation" is a heat map, how could I specify this "dual-time" nature of the chart. So far, "bar chart" the best generalization, but it doesn't specify these features. $\endgroup$ Commented May 25 at 11:36
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    $\begingroup$ The dual-time component is characteristic of a raster plot. See the example in the (non-paywalled) article here: academic.oup.com/sleep/article/44/10/zsab103/6232042 $\endgroup$
    – AdamO
    Commented Jun 5 at 4:31
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General riff (skip or skim according to taste)

Names should not matter, except that they do. A good name can be vivid, encouraging and even entertaining. A poor name can seem obscure or confuse or even condemn a good idea to oblivion.

It can be both highly positive and highly negative if a particular kind of chart is named for people in one field who made a fuss about it. We should want to honour people who did innovative work, but the history is often wrong. And those names may mean little or nothing to people outside that field.

Further, people typically want to know not just what a graph is (generally or widely) called but also what name is used within particular software. Those two are often not close!

Surprisingly often, graphs don't have standard names, fixed across time or across disciplines. Even a simple and common term, such as bar chart, need not have a fixed meaning. A definition or usage that still lingers is that a bar chart has horizontal bars, but a chart with vertical bars should be called a column chart. (If you think that's silly, or at least not a distinction worth making, I happen to agree, but arguing that such usage is wrong is also futile.) Is a histogram a bar chart? Many statistical people want to say No emphatically, but graphically or geometrically a histogram to me (usually) is a bar chart; I just wouldn't try to call a histogram a kind of bar chart in anything I write, because of the opposite point of view.

Is a line chart defined by connected lines? I can cite examples of strip plots presented as a series of points on a number line that are called line charts.

Are there differences between charts, diagrams, graphs and plots? I have seen attempts to distinguish them that are utterly unconvincing. There doesn't seem to be rhyme or reason behind what is called what, except what was loosely fashionable at the time a term was introduced. Similarly, few now feel compelled to reach for a Greek or Latin dictionary to invent a word; in contrast, simple words recalling simple things have been in favour for some time (box, strip, violin).

What might be called chart choosers often show a series of different chart types with suggested names and/or suggested uses. Such choosers may be helpful, but choice in statistical graphics is not like choosing paint colours or wallpaper or fabric patterns from a finite catalogue, however large. No experienced person or expert quite likes anyone else's chooser: the names are poor, the recommendations are poor, the chooser is incomplete, the chooser omits hybrid designs, or whatever.

A different name for every minutely different chart type wouldn't help if only because clear examples are always worth much more than an elaborate terminology.

Is this a heat map?

I can see why people want to call this a heat map. Reservations on various different levels:

  • That isn't a historic term. It appears to be relatively new.

  • Some people might reserve heat maps for something with underlying matrix form in which discrete cells are coloured differently.

  • Heat maps are greatly oversold. (I'll leave that as opinionated assertion.)

Is this just another bar chart?

To me this is (also) just one more flavour of a bar chart. Bars represent time intervals. Intervals are stacked. What else needs to be explained? In software I know best, it would be coded as a kind of bar chart.

In some fields a name like Gantt chart has stuck. At least that is easy to Google if you want to know more. In examples I recall different codings on a Gantt chart represent qualitatively different tasks, but who cares about ordered scales too?

Historically, that name reflects strong advocacy from Gantt but is also absurd. Bar charts broadly like those have been used for some centuries to show (e.g.) lifetimes of famous people, reigns of monarchs or other heads of state, and so forth for some centuries, predating even William Playfair's bar charts. For a dedicated treatment at book length, see https://www.amazon.com/Cartographies-Time-Timeline-Anthony-Grafton/dp/1568987633

I quite often see similar plots used now for television or radio schedules.

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    $\begingroup$ Well, thank you for the detailed explanation. First of all, I couldn't agree more that terms devoted to people are mostly confusing rather than helping. In all areas. On the other hand, a good name could help to make negotiations shorter and that's what most of terms do in domain areas. When we say "pie chart" most people are on the same page with the expectations; at least for a starter. So, the only thing I want to avoid is to confuse people when I ask about a diagram with words like "such and such" instead of heatmap. Like a common name for starters. $\endgroup$ Commented May 24 at 13:05
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    $\begingroup$ I am not sure that this is a Gantt chart by the reasons I mentioned in the comments to more precise question: What do they call such a chart with a strip of activity types per time?. Again, I see that it is quite close, but if I ask on form that I want a Gantt chart, in this particular case this will be more confusing rather than helping. So, I again agree with you initial message here. $\endgroup$ Commented May 24 at 13:07
  • $\begingroup$ Oddly enough, the name pie chart only rather suddenly become popular around 1920, many years after the idea was first mooted. It's not universal even now, but it is (jn my reading) a strong majority term. (Nevertheless pie charts should be shunned.) $\endgroup$
    – Nick Cox
    Commented May 24 at 13:10
  • $\begingroup$ I like the "bar chart" name as the answer to the question I wanted to ask What do they call such a chart with a strip of activity types per time? instead one I mistakenly asked here. Thank you. For this one (my initial wording here), I would agree with heatmap more. But, as you stated, this is a matter of preference, of course. $\endgroup$ Commented May 24 at 13:12
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    $\begingroup$ I believe, this is a reasonable point for any particular representation of information, since most for them do kinds of projections with reducing/packing information or looking from a different perspective and only some of them extend the number of dimensions. In such cases, of course, any particular view should be suitable for the task to be solved. No doubts. $\endgroup$ Commented May 24 at 18:26

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