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<title>CSS Slope Graphs</title>
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<h1 id="css-slope-graphs">CSS Slope Graphs</h1>
<p>2021-06-07</p>
<p><em>I am a huge sucker for simplistic and beautifully designed visual data on the web</em>. Most data tends to be graphed via line or bar systems - which is fine - but I think slope graphs are highly underrated. Let’s change that, shall we?</p>
<h2 id="the-demo">The Demo</h2>
<p>I’m basing this demo off the design patterns found in <a href="https://www.edwardtufte.com/tufte/books_vdqi">Edward Tufte’s visualization work</a>, specifically his slope graph designs:</p>
<p><a href="https://codepen.io/bradleytaunt/pen/jOBzXMe">Live CodePen Example</a></p>
<h2 id="the-html">The HTML</h2>
<p>For this concept we will actually be building this graph out of <code>tables</code> - crazy, right? The greatest benefit of rendering all the data inside of a <code>table</code> element is the ability to easily support smaller screens and mobile devices. Larger viewports will get to see the pretty slope graph, while those below a certain threshold will view a simple table.</p>
<p>(But more on that in the CSS section)</p>
<pre><code><p>Sales of the leading frozen pizza brands of the United States from 2011 to 2017 (in million US dollars) <br><em>Source: Statisa 2018</em></p>
<table>
<thead>
<tr>
<th>Pizza Brand</th>
<th>2011</th>
<th>2017</th>
</tr>
</thead>
<tbody>
<tr>
<td data-set="677.0">DiGiorno</td>
<td><span>677.0</span></td>
<td data-name="DiGiorno">1014.6</td>
</tr>
<tr>
<td data-set="294.8">Private Label</td>
<td><span>294.8</span></td>
<td data-name="Private Label">524.8</td>
</tr>
<tr>
<td data-set="286.1">Red Baron</td>
<td><span>286.1</span></td>
<td data-name="Red Baron">572.3</td>
</tr>
<tr>
<td data-set="257.9">Tombstone</td>
<td><span>257.9</span></td>
<td data-name="Tombstone">270.6</td>
</tr>
<tr>
<td data-set="164.5">Totino's Party Pizza</td>
<td><span>164.5</span></td>
<td data-name="Totino's Party Pizza">347.2</td>
</tr>
</tbody>
</table>
</code></pre>
<p>As you can see, nothing too fancy is happpening here. Pay close attention to the <code>data-set</code> and <code>data-name</code> variables though - those will be important for the CSS portion of this design, mainly the rendering of the line elements.</p>
<h2 id="the-css">The CSS</h2>
<p>To avoid overwhelming your brain all-at-once, let’s break the CSS down into bite-sized chunks, starting with the base styling:</p>
<pre><code>@import url('https://opentype.netlify.com/et-book/index.css');
* {
box-sizing: border-box;
}
html {
height: 100%;
}
body {
background: #fffff8;
font-family: "et-book", serif;
height: 100%;
margin: 0 auto;
max-width: 800px;
padding: 0 0.5rem;
}
p {
font-size: 18px;
margin: 4rem 0 6rem;
}
table {
border-collapse: collapse;
text-align: left;
width: 100%;
}
</code></pre>
<p>Pretty basic stuff.</p>
<p>Now we need to design how our slope graph will look on larger screens / desktops. For this instance, we will target these larger devices with a <code>min-width</code> media query of <code>800px</code>. The rest of the CSS might look a little confusing but I assure you it is quite simple.</p>
<ol>
<li><p>On larger devices we hide the first <code>thead tr th</code> element with <code>display: none</code></p></li>
<li><p>The first and second <code>td</code> elements inside each <code>tbody</code> row need to be set as <code>position: absolute</code> to avoid duplicate content</p></li>
<li><p>The inner <code>span</code> that we include in our HTML inside the second <code>tbody tr td</code> also needs to be <code>display: none</code></p></li>
<li><p>Remember that <code>data-set</code> variable? We now use that for our <code>:before</code> pseudo element for <code>table tbody tr td:nth-of-type(1)</code></p></li>
<li><p>Remember that <code>data-name</code> variable? We now use that for our <code>:before</code> pseudo element for <code>table tbody tr td:nth-of-type(3)</code></p></li>
<li><p>After that, you can see the simple customization we include to render the angle / position of the slope lines and the corresponding labels</p>
<p>@media(min-width:800px) {
table {
display: block;
position: relative;
margin-bottom: 25rem;
}</p>
<pre><code>table thead th {
border-bottom: 1px solid lightgrey;
font-size: 24px;
position: absolute;
top: -50px;
width: 45%;
}
table thead th:nth-child(1){ display: none; }
table thead th:nth-child(2){ left: 0; }
table thead th:nth-child(3){ right: 0; text-align: right; }
table tbody tr td:nth-of-type(1),
table tbody tr td:nth-of-type(2) { position: absolute;}
table tbody tr td:nth-of-type(2) span { display: none; }
table tbody tr td:nth-of-type(1):before {
content: attr(data-set);
margin-right: 10px;
position: relative;
}
table tbody tr td:nth-of-type(2) { padding-left: 10px; }
table tbody tr td:nth-of-type(3) {
position: absolute;
right: 0;
}
table tbody tr td:nth-of-type(3):before {
content: attr(data-name);
margin-right: 10px;
position: relative;
}
/* Custom individual slopes -- Left */
tbody tr:nth-child(1) td:nth-child(1),
tbody tr:nth-child(1) td:nth-child(2) { top: 60px; }
tbody tr:nth-child(2) td:nth-child(1),
tbody tr:nth-child(2) td:nth-child(2) { top: 140px; }
tbody tr:nth-child(3) td:nth-child(1),
tbody tr:nth-child(3) td:nth-child(2) { top: 165px; }
tbody tr:nth-child(4) td:nth-child(1),
tbody tr:nth-child(4) td:nth-child(2) { top: 220px; }
tbody tr:nth-child(5) td:nth-child(1),
tbody tr:nth-child(5) td:nth-child(2) { top: 270px; }
/* Custom individual slopes -- Right */
[data-name="DiGiorno"] { top: 0; }
[data-name="Red Baron"] { top: 65px; }
[data-name="Private Label"] { top: 100px; }
[data-name="Tombstone"] { top: 180px; }
[data-name="Totino's Party Pizza"] { top: 150px; }
/* The custom visual lines */
tbody tr:after {
background: black;
content: '';
height: 1px;
left: 14.5%;
position: absolute;
width: 70%;
}
tbody tr:nth-child(1):after {
top: 40px;
transform: rotate(-6deg);
}
tbody tr:nth-child(2):after {
left: 17.5%;
top: 130px;
transform: rotate(-4deg);
width: 65%;
}
tbody tr:nth-child(3):after {
left: 15%;
top: 125px;
transform: rotate(-10.25deg);
width: 70%;
}
tbody tr:nth-child(4):after {
left: 16%;
top: 210px;
transform: rotate(-4deg);
width: 68%;
}
tbody tr:nth-child(5):after {
left: 22%;
top: 222px;
transform: rotate(-16deg);
width: 56%;
}
</code></pre>
<p>}</p></li>
</ol>
<p>All that’s left are some minor styles to make everything look nice on mobile:</p>
<pre><code>@media(max-width:800px) {
p {
margin: 2rem 0;
}
table td, table th {
border-bottom: 1px solid grey;
padding: 10px;
}
table td:last-of-type, table th:last-of-type {
text-align: right;
}
}
</code></pre>
<h2 id="not-the-most-practical">Not the most practical</h2>
<p>This slope graph concept is far from perfect for use in real-world situations. The fact that you need to manually render each point of data yourself makes this implementation quite annoying for more in-depth projects.</p>
<p>But it was fun to mess around with and create, so who cares!</p>
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