Bar chart

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

## Overview

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A bar chart, also known as a bar graph, is a chart with rectangular bars of lengths usually proportional to the magnitudes or frequencies of what they represent. Bar charts are used for comparing two or more values. The bars can be horizontally or vertically oriented. Sometimes a stretched graphic is used instead of a solid bar.

## Example

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The example chart is based on the results of the election for the European Parliament in 2004 and in 1999. The following table lists the number of seats allocated to each party group. The results of 1999 have been multiplied by 1.16933, to compensate for the change in number of seats between those years.

Group  | Seats (2004)  | Seats (1999) scaled

|
|

EUL  | 39  | 49
PES  | 200  | 210
EFA  | 42  | 56
EDD  | 15  | 19
ELDR  | 67  | 60
EPP  | 276  | 272
UEN  | 27  | 36
Other  | 66  | 29

A bar chart visualizing the above results of the 2004 election can look like this:
(If all the values were arranged in descending order this type of bar graph would be called a pareto chart.)

<timeline> ImageSize = width:400 height:240 PlotArea = width:300 height:150 left:50 bottom:40 AlignBars = late

DateFormat = yyyy Period = from:0 till:300 TimeAxis = orientation:vertical ScaleMajor = unit:year increment:50 start:0

BarData=

bar:1 text:"EUL"
bar:2 text:"PES"
bar:3 text:"EFA"
bar:4 text:"EDD"
bar:5 text:"ELDR"
bar:6 text:"EPP"
bar:7 text:"UEN"
bar:8 text:"Other"

Colors =

id:lightgrey value:gray(0.7)
id:darkgrey  value:gray(0.1)

TextData =

pos:(10,220) textcolor:black fontsize:S
text:Seats
pos:(180,25) textcolor:black fontsize:S
text:Group
pos:(90,225) textcolor:black fontsize:M
text:European Parliament Election 2004

PlotData=

width:18
bar:1 color:lightgrey from:0 till:39
bar:2 color:lightgrey from:0 till:200
bar:3 color:lightgrey from:0 till:42
bar:4 color:lightgrey from:0 till:15
bar:5 color:lightgrey from:0 till:67
bar:6 color:lightgrey from:0 till:276
bar:7 color:lightgrey from:0 till:27
bar:8 color:lightgrey from:0 till:66

</timeline>

This bar chart shows both the results of 2004, and those of 1999:

<timeline> ImageSize = width:480 height:240 PlotArea = width:360 height:150 left:50 bottom:40 AlignBars = late

DateFormat = yyyy Period = from:0 till:300 TimeAxis = orientation:vertical ScaleMajor = unit:year increment:50 start:0

BarData=

bar:17 text:
bar:2 text:
bar:1 text:
bar:17 text:
bar:4 text:
bar:3 text:
bar:17 text:
bar:6 text:
bar:5 text:
bar:17 text:
bar:8 text:
bar:7 text:
bar:17 text:
bar:10 text:
bar:9 text:
bar:17 text:
bar:12 text:
bar:11 text:
bar:17 text:
bar:14 text:
bar:13 text:
bar:17 text:
bar:16 text:
bar:15 text:

Colors =

id:lightgrey value:gray(0.7)
id:darkgrey  value:gray(0.4)

TextData =

tabs:(28-center,74-center,118-center,164-center,211-center,254-center,300-center,347-center)
pos:(10,220) textcolor:black fontsize:S
text:Seats
pos:(200,25) textcolor:black fontsize:S
text:Group
pos:(130,225) textcolor:black fontsize:M
text:European Parliament Elections
pos:(233,193) textcolor:black fontsize:S
text:2004
pos:(185,193) textcolor:black fontsize:S
text:1999
pos:(50,40) textcolor:black fontsize:S
text:^EUL^PES^EFA^EDD^ELDR^EPP^UEN^Other

PlotData=

width:0
bar:1 color:lightgrey from:0 till:39 width:15
bar:2 color:darkgrey from:0 till:49 width:15
bar:3 from:0 till:200 width:15 color:lightgrey
bar:4 color:darkgrey from:0 till:210 width:15
bar:5 from:0 till:42 width:15 color:lightgrey
from:280 till:300 color:darkgrey width:10
bar:6
from:0 till:56 width:10 color:darkgrey width:15
bar:7
from:0 till:15 width:15 color:lightgrey
from:280 till:300 color:lightgrey width:10
bar:8 color:darkgrey from:0 till:19 width:15
bar:9 color:lightgrey from:0 till:67 width:15
bar:10 color:darkgrey from:0 till:60 width:15
bar:11 color:lightgrey from:0 till:276 width:15
bar:12 color:darkgrey from:0 till:272 width:15
bar:13 color:lightgrey from:0 till:27 width:15
bar:14 color:darkgrey from:0 till:36 width:15
bar:15 color:lightgrey from:0 till:66 width:15
bar:16 color:darkgrey from:0 till:29 width:15

</timeline>

## History

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The bar chart is possibly the invention of the Scots engineer and economist William Playfair (1759-1823). A bar chart was used in his work The Commercial and Political Atlas (London, 1786).

## See also

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* Histogram -- a special type of bar chart.
* Gantt chart
* Pie chart

## External links

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* "bar graphs in Javascript".

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