Design Recommendations for Chart Types

Area Chart

Figure 1: Area chart

Figure 2: Multiple column chart

The baseline of a bar chart or column chart consists of labels (e.g. customers, regions, products), not a numerical scale, even if it sometimes looks like that.
Types:
- Column Chart: Vertical columns
  - Use if the values are more important than the labels (e.g. years)
- Bar chart: Horizontal bars
  - Use if the labels for the data are very long
  - Use if the information is more important than the values themselves -> the labels are to the left and are read first
Column/bar charts can be used to compare more than one category at a time -> multiple column/bar charts.
Separate columns/bars through white space (for more than one categories, only the groups are separated through white space)
Choose an organizational principle for the baseline:
- Time, e.g. costs from January to December
- Quantity or volume, e.g. number of sold units
- Alphabet
- None: order columns/bars according to rank in ascending or descending order
If possible show comparison values like a "baseline" value or a "critical" value
If applicable and possible show error limits

Add labels to axes and columns/bars: Place scale and marks at the axis, label below (columns) or left to (bars) the baseline.
For multiple column charts:
- Place group labels below the baseline, left-aligned to the columns
- Column labels:
  - Place label for each column type into the diagram area or
  - Use shading or patterns plus a key to identify the columns
Label multiple bar charts analogously
Bar charts
- Short labels: Place labels to the left
- Long labels: Right-align labels to the right chart border

Use a unique color or pattern for each value; use a contrast of at least 30% between neighboring columns or bars
Striped patterns: Use patterns with an angle of 45° to the base line in order to avoid optical illusions; let the stripes all go into the same direction
Better: Avoid striped patterns and use solid colors or grays
If possible use colors or patterns that emphasize the data with similar meaning, e.g. red for "critical" or "red shirt"

Figure 3: Segmented column chart (relative values)

For scales, axes and layout see column/bar charts
Arrange segments within each column/bar in the same order
Do not place labels into the segments. Place them right beside the diagram or above it - or use a legend. Do not label each column/bar
If possible, place the segment with the least change lowest and the most variable at the top; for bars do the analog. This arrangement makes comparison easier and emphasizes changes
Make the segments easy to distinguish; use the most striking color or pattern for the most important data
Limit the number of segments to those that are large enough to be easily recognized and labeled; combine small segments into a larger one

Figure 4: Line chart

Use the Y axis for variable (dependent), the X axis for fixed (independent) information
For comparisons of data sets, draw each data set as a graph of its own in a common line chart (not more than 4-5 graphs - otherwise split data sets into several charts:
- For example, compare the most important graph with every other graph
- Plot the most important graph against a small set of other relevant graphs
There are no rules for the interval size of the axes; however, the graph should be neither too steep nor too flat
Label each graph, if possible (otherwise use keys)
If appropriate, display a reference line
For multiple graphs: Use symbols for the data points to visually set the graphs apart; make the symbol 2-3 times larger then the line

If there are several graphs within one chart, use colors or line styles to distinguish the lines (care for overlapping graphs)
Emphasize the most relevant graph, if applicable, by using the most striking color or the thickest lines for it
If lines cross each other, interrupt the background lines

Figure 5: Pie chart

Start at 12 o clock (top), then follow the direction of the clock
The values must add up to 100% (or have to be scaled accordingly)
Do not use too small circle segments (> 18° or 5%); combine small segments intro larger ones, if applicable
Label each segment
Labels can be placed within segments (if these are large enough and the labels short) or outside (small segments, long labels)
Write the values beside the segments, because angles are hard to estimate

Use highlighting methods only, if really necessary. Typical emphasizings are:
- Pull a segment out of the pie
- Use different colors or patterns
Patterns: Try to alternate between patterns and solid colors; avoid vibrating patterns or patterns that produce optical illusions.
Use perspective only, if distortions are tolerable (write values beside the segments in this case).

Figure 6: One-dimensional scatterplot (left), two-dimensional scatterplot (right)

Preferably use a square for the diagram; for two-dimensional scatter plots both axes should have identical scale divisions
Use different symbols, if different sets of data are included in one scatter plot:
- Useful symbols are:
  ;
  Less useful symbols are:
- Different colors help to distinguish symbols; circles are good distinguishable from triangles, but not good distinguishable - especially if small - from squares
- Colors may be used "symbolically", e.g. = "without treatment", = "with treatment"
- All symbols should be of the same size - or at least look as if they were of same size (sometimes optical corrections are necessary)
- Use overlapping symbols for overlapping data points, not just one symbol
- Identical data points should be represented through special symbols which indicate this fact
Important or critical data points should be highlighted, e.g. though more intensive color, a different color or a different shape
If data points lie on the axes, move the axes slightly outwards