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A bar chart is a diagram, presenting comparable data in discrete categories in the form of rectangular bars, that have either their heights or lengths proportional to the represented values. Generally, it consists of two axis. A nominal axis, showing the compared categories and an interval scaled axis, representing the measured value.
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Beside the bar direction which can either be *vertical or horizontal*, two more properties will be distinguished for further considerations. First the diagram orientation, which is either *landscape or portrait* and second the distinction of categories, which can either be done by *axis labels or distinct textures*.
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##### A uniform bar texture
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For categories which are distinguished by an axis label there is no need for distinct textures. As seen before, the availability of different line styles is very limited because of a lower resolution compared to tactile printing, but still use of line styles can be made to create a uniform texture, that provide an implicit scale to determine the bar size even when the axis is far away.
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The uniform texture is basically a simple line pattern, either horizontal or vertical depending on the axis rotation, with intermediate dotted lines. The following depiction shows an example bar with the normal 'vertical_line' texture on top of a bar with the modified texture.
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![uniform_bar_texture](uploads/7dab95c50477937733885cfcc43dfebc/uniform_bar_texture.png)
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The uniform texture can be applied as long as the spacing between the axis divisions (tickmarks) is an even number of (at least 4) dots. The texture is applied by aligning the solid lines with the tickmarks. In this way, the texture allows to distinguish between whole and half unit steps.
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##### Basic bar chart prototype
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All depictions of the bar chart prototypes are generated using a software called 'QuickTac' by Duxbury Systems.
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![bar_charts_landscape](/uploads/1f22e924a5967161e15cf44fe2c7f68d/bar_charts_landscape.png)
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The given prototype shows a bar chart with uniform textured horizontal bars on an A4 sheet in landscape orientation. Of course, many other chart arrangements with varying advantages and disadvantages are possible.
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##### Investiagtion of different chart arrangements
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In the following, an exemplary comparison of different arrangements and their impact on the depcitable amount of information is given.
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The arrangement of a bar chart depends on three relevant properties, while charts with vertically oriented bars are sometimes called line charts instead of bar charts. This will be ignored for the sake of simplicity:
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```mermaid
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graph TD;
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bar_chart-->orientation;
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bar_chart-->direction;
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bar_chart-->textures;
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orientation-->landscape;
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orientation-->portrait;
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direction-->vertical;
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direction-->horizontal;
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textures-->uniform;
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textures-->distinct;
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```
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Technically the maximum amount of categories with distinct textures is limited by the amount of available textures. This is problematic, because appropriate distinguishable textures are rare when dealing with such low resolution.
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The width of bars with distinct texture is assumed to be 9 dots.
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Bars with uniform texture are described by 4 braille characters; horizontal: 5 dots wide, 1 dot spacing; vertical: 13 dots wide, 1 dot spacing.
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The axis units are 4 dots apart.
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Since changes of the resolution change the values linearly, this table can be used to compare the different arrangements.
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<table>
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<thead>
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<tr>
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<th colspan=3>Properties</th>
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<th colspan=2>Diagram area</th>
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<th colspan=2>Max. possible:</th>
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</tr>
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<tr>
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<th>Orientation</th>
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<th>Direction</th>
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<th>Textures</th>
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<th>width (dots)</th>
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<th>height (dots)</th>
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<th># Categories (Bars)</th>
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<th># Axis divisions</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td rowspan=4>landscape</td>
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<td rowspan=2>horizontal</td>
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<td>uniform</td>
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<td>93</td>
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<td>56</td>
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<td>9</td>
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<td>23</td>
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</tr>
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<tr>
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<td>distinct</td>
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<td>105</td>
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<td>56</td>
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<td>5 (4)</td>
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<td>26</td>
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</tr>
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<tr>
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<td rowspan=2>vertical</td>
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<td>uniform</td>
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<td>106</td>
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<td>54</td>
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<td>7</td>
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<td>13</td>
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</tr>
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<tr>
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<td>distinct</td>
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<td>106</td>
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<td>58</td>
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<td>10 (4)</td>
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<td>14</td>
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</tr>
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<tr>
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<td rowspan=4>portrait</td>
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<td rowspan=2>horizontal</td>
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<td>uniform</td>
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<td>59</td>
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<td>90</td>
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<td>14</td>
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<td>14</td>
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</tr>
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<tr>
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<td>distinct</td>
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<td>71</td>
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<td>90</td>
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<td>8 (4)</td>
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<td>17</td>
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</tr>
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<tr>
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<td rowspan=2>vertical</td>
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<td>uniform</td>
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<td>72</td>
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<td>88</td>
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<td>5</td>
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<td>22</td>
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</tr>
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<tr>
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<td>distinct</td>
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<td>72</td>
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<td>92</td>
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<td>7 (4)</td>
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<td>23</td>
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</tr>
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</tbody>
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</table>
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So the best arragement depends on how much categories have to be depicted in the chart and which value resolution is desired. |
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