## Overview of Chart Types and their Uses

Chart Type |
PIG |
Typical Applications |
Variants, Remarks |
---|---|---|---|

Area |
Yes | Cumulated totals (numbers or percentages) over time | Percentage, Cumulative |

Column/Bar |
Yes | Observations over time or under different conditions; data sets must be small | Vertical (columns), horizontal (bars); multiple columns/bars, columns/bars centered at zero |

Segmented Column/Bar |
Yes | Proportional relationships over time | May be scaled to 100% |

Frequency Polygon |
No | Discrete frequency distribution | |

Histogram |
No | Discrete frequency distribution | Columns/bars without gaps |

Line, Curve |
Yes | Trends, functional relations | Data point connected by lines or higher order curves |

Pie |
Yes | Proportional relationships at a point in time | Segments may be pulled out of the the pie for emphasis (exploded pie chart) |

Scatterplot |
No | Distribution of data points along one or two dimensions | One-dimensional, two-dimensional |

Map |
No | Typically used for geographical data; can also be used for parts of devices, human or animal bodies | Useful, if an analog relation can be used for representing data |

The column PIG indicates whether the respective charts types are available as Portable Interactive Graphics.

## Area Chart

**Figure 1**: Area chart

### Use it to…

- Display over time (or any other dimension):
- How a set of data adds up to a whole (cumulated totals)
- Which part of the whole each element represents

### Variants

**Percentage**: The sum always represents 100% (relative scale)**Cumulative**: The sum can vary according to the elements (absolute scale)

## Column/Bar Chart

### Use it to…

- Present few data over a nominal (e.g. countries, testing conditions, …) or interval scale (e.g. time); useful for comparisons of data

**Do not Use it for…**

- Comparisons: Better use one-dimensional scatterplots, because these are not dominated by bars or columns.
- Larger data sets: Use line charts.

### Selecting Bars or Columns

- Use analogy as a selection criterion, if applicable; when in doubt, use columns
- Use a horizontal bar chart if the labels are too long to fit under the columns

### Variants

**Multiple Column/Bar Chart**: Use it to present data rows for several variables**Side-by-Side Chart**: Use it to (1) show contrasting trends between levels of an independent variable, (2) if comparisons between individual pairs of values are most important; do**not**use for more than two independent variables

**Figure 2**: Multiple column chart (left), side-by-side chart (right)

## Segmented Column/Bar Chart

**Other Names**: Divided or stacked column/bar chart

**Figure 3**: Segmented column chart (relative values)

### Use it to…

- Present a part-whole relation over time (with accurate impression, see below)
- Show proportional relationships over time
- Display wholes which are levels on a nominal scale

Segmented column/bar charts are more accurate than pie chart, because distances can be more accurately estimated than areas.

## Frequency Polygon, Histograms

**Figure 4**: Histogram as frequency distribution

### Variants

**Polygon**: Connects data points through straight lines or higher order graphs**Histogram**: Columns/bars touch; useful for larger sets of data points, typically used for frequency distributions**Staircase Chart**: Displays only the silhouette of the histogram; useful for even larger sets of data points, typically used for frequency distributions**Step chart**: Use it to illustrate trends among more than two members of nominal or ordinal scales; do**not**use it for two or more variables or levels of a single variable (hard to read)**Pyramid histogram**: Two mirror histograms; use it for comparisons

## Line Chart

**Figure 5**: Line chart

### Use it…

- To display long data rows
- To interpolate between data points
- To extrapolate beyond known data values (forecast)
- To compare different graphs
- To find and compare trends (changes over time)
- To recognize correlations and covariations between variables
- If the X axis requires an interval scale
- To display interactions over two levels on the X axis
- When convention defines meaningful patterns (e.g. a zigzag line)

Line graphs may consist of line or curved segments:

- Lines: Use straight lines to connect “real” data points
- Curves: Use curves to represent functional relations between data points or to interpolate data

### Do not Use it…

- If the X axis has non-numeric values

### Variants

- Graph with
**double-logarithmic**or**half-logarithmic**scale divisions - Graph with variance bars, stock charts (High/Low/Close) etc.

## Pie Chart

**Figure 6**: Pie chart

### Use it to…

- convey approximate proportional relationships (relative amounts) at a point in time
- compare part of a whole at a given point in time
- Exploded: emphasize a small proportion of parts

### Do not Use it …

- For exact comparisons of values, because estimating angles is difficult for people.
- For rank data: Use column/bar charts in this case; use multiple column/bar charts for grouped data
- If proportions vary greatly; do not use multiple pies to compare corresponding parts.

### Caution!

- Pie charts cannot represent values beyond 100%.
- Each pie chart is valid for one point in time only.
- Pie charts are only suited to presenting quite a few percentage values.
- Angles are harder to estimate for people than distances; perspective pie charts are even harder to interpret.

## Scatterplot

**Figure 7**: One-dimensional scatterplot (left), two-dimensional scatterplot (right)

### Variants

**One-dimensional scatterplot**: Data point are drawn above a baseline (as in column/bar charts). Here the data points are not connected but remain isolated data points.**Two-dimensional scatter plot**: Shows correlation between two data sets. This chart type has two dependent variables: One is plotted along the X axis, the other along the Y axis; the independent variable is the intersection of both dependent variables, realized as a data point in the diagram.

### Use it to…

- Show measurements over time (one-dimensional scatterplot)
- Convey an overall impression of the relation between two variables (Two-dimensional scatterplot)

### Do not Use it for…

- Determining and comparing trends, interpolation, extrapolation, recognition and comparison of change rates
- More than one independent variable: Avoid illustrating more than one independent variable in a scatter plot

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