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A lot of research has been done on tactile graphics and the subcategory tactile diagrams.
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The main idea behind this projects concept is the translation of diagrams into a format that is printable on a braille embosser, from now on called braille diagrams in contrast to other forms of 'tactile diagrams' which are meant to be printed on a tactile printer.
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Similar projects have already been done but most focus on the braille based representation of graphics in a way equivalent to ASCII art and there is not nearly as much information about the criteria for 'good' braille diagrams, as there is for tactile diagrams. How can guidelines regarding the creation of tactile diagrams be applied on braille diagrams?
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Main differences
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The usage of braille embossers instead of tactile printers introduces some differences that have an impact on the design of diagrams (and graphics in general), some depending on the embossers abilities:
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- reduced resolution
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- no equidistant grid
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- no different intensity levels
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- smaller print area
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The main consequences are:
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- lower information density (e.g. fewer diagram elements)
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- fewer styling options (textures, line-thickness, ...)
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- less overall space
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Known guidelines
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The following papers and guidelines have been taken into account for this concept:
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- Engel, C. Kriterien zur Erstellung taktiler Diagramme und Diagrammbeschreibungen. [online] Available at: https://tu-dresden.de/ing/informatik/ai/mci/forschung/forschungsgebiete/mosaik-zugaengliche-grafiken-fuer-und-von-blinden-nutzern [Accessed 16.05.2019].
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- Prescher, D. and Bornschein, J. (2016). Richtlinien zur Umsetzung taktiler Grafiken. [online] Available at: http://www.qucosa.de/fileadmin/data/qucosa/documents/19616/PDF_A_1b_Richtlinien_TaktileGrafiken_accessible.pdf [Accessed 17.05.2019].
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A complete list of criteria for tactile diagrams that are partially derived from general criteria regarding tactile graphics is given in 'Kriterien zur Erstellung taktiler Diagramme und Diagrammbeschreibungen.'. (Engel, C.) In the following, the given definitions from this list are applied under the previously identified differences when using braille embossing instead of tactile printing. Most guidelines can be directly applied to our use case, but there are some specific particularities.
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The dot spacing has an impact on the maximum resolution, thicknesses and lengths. For the following list, the 6-dot braille ANSI standard ('American National Standard: Accessible and Usable Buildings and Facilities: 2003: Standard and Commentary. ICC/ANSI A117.1-2003. P151-163.', https://codes.iccsafe.org/content/ICCA117_12003/chapter-7-communication-elements-and-features#ICCA117.1_2003_Ch07_Sec703) is assumed, but on an equidistant grid. This means that between all neighboring dots a vertical and horizontal distance of 2.5mm from center to center is assumed. Dots have a diameter of 1.5mm. There are no additional distances between symbols and lines.
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| Element | Description | Braille particularities |
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| ------- | ----------- | ----------------------- |
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| **Title** | in braille, containing diagram type
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|| top-left horizontal alignment
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|| maximum of 2 lines
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| **Axis** | 'continuous' lines | no real continuous line possible
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|| requirement for tactile diagrams is minimum thickness of 1 mm | such small resolutions are not possible with braille. Instead, use thickness of 1 dot (1.5mm)
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|| axis name (possibly including unit) in braille
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|| value range divided by tickmarks, values in braille
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| **Legend** | on separate sheet | depiction on same sheet mostly impossible because of lack of space
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|| repeat diagram title for association
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|| label as legend
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|| legend symbols left aligned, right-hand captions
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|| minimum symbol size: 25mm height x 12.5mm width | corresponds to 10 x 5 dots.
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|| symbol group order: area-textures, line-styles, point-symbols, alphabetic keys, numeric keys
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|| order inside groups corresponding to occurence in reading direction
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|| symbols on equivalent scale on both sheets
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| **Gridlines** | only if necessary for context, with recommended grid size of 20mm | corresponds to 8 dots
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|| lower resolution than axis tickmarks possible
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|| clearly distinguishable from other diagram contents | problem: few line-styles available, consider 'negative' lines
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|| grid should be explained in legend
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| **Captions** | no other captions in diagram area beside from: title, axis names, axis values
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|| braille always horizontally aligned
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| **Annotations** | describe context, remarks and adaptions of the diagram | same space problem as with legend, consider placing annotations on separate sheet or maybe on legend sheet if possible.
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Design options
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### Line styles
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The following example shows simple different line styles that are realized with dots on an equidistant grid. The lines differ in thickness from 1 to 3 dots (1.5mm - 6.5mm) and each thickness is depicted as solid, dotted and dashed variant.
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![Braille line styles](bar_charts/figures/lines.PNG)
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Taking the low resolution of the grid into account, it becomes clear, that thicker lines become impracticable very soon. For a thickness of 3 dots, a single line dash already has a length of 1.4 centimetres in this example and the line consumes a lot of space. For our specific use case, styling options for lines of the smallest thickness (1 dot) are interesting, they can especially be used to enhance textures.
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### Textures
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A set of basic recommended textures for tactile graphics (Prescher, D. and Bornschein, J., 2016) has been applied to the dot grid in the example below, by filling a 10 by 10 square (2.4cm sidelength) with the respective texture. The exact pattern spacings had to be manipulated partially, because of the lower resolution. From left to right, the depicted textures in the upper row are called 'full_pattern', 'horizontal_line', 'vertical_line', 'diagonal_line1' and 'diagonal_line2'. The lower row shows the textures 'dashed_lines', 'grid_pattern', 'dotted_pattern', 'stair_pattern' and an empty box for comparison.
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![Braille textures](bar_charts/figures/textures.PNG)
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The original purpose of the textures - to create distinguishable areas on a tactile graphic - is of course relevant for this specific use case, but it has to be extended further. Since it is hard to add reqular gridlines to a braille diagram, the texture should also be suitable to give an implicit scale, so that the dimensions of a tactile object can also be determined if the object is far from the nearest axis. (For example in a bar chart.)
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For this purpose, a texture needs to include a distinguishable consistent component, that is orthogonal to the coordinate systems axis and can be aligned with the axis units. For this reason, the full_pattern (no distinguishable components inside), the diagonal_line textures (not orthogonal) as well as the stair_pattern (orthogonal but not consistent) aren't suited.
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The remaining textures are the 'dotted_pattern', 'dashed_lines', 'horizontal_line' or rather 'vertical_line' - depending on the orientation of the measured dimension - as well as the 'grid_pattern' which is 90 degree rotationally symmetric and can 'measure' both dimensions at once, since it is essentially a regular grid line.
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Concept prototypes
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The following prototypes are designed under the criteria from the previous list. A standard A4 sheet (297mm x 210mm) with a 10mm margin from all sides is assumed as available area for the diagram and the same for the legend. This leaves an area of 110 dots x 76 dots per sheet.
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### General template
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### Bar charts
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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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![Bar chart prototype](bar_charts/figures/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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- Dealing with negative values -> move axis inside diagram area, better to not have the concrete values on the axis, but instead explained on legend, also for space reasons (give example of numeric values)
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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 chart prototype](bar_charts/figures/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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##### How to choose an appropriate arrangement
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The arrangement of a bar chart depends on three relevant properties:
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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. (currently 4)
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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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### Line charts
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### Scatter plots |
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