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Allow bar graph as well as line graph #2608
Quick explanation: line charts are for continuous data, bar charts are for discrete data. The numbers of visits per day is a classic example of discrete data and therefore a bar chart would be the right chart.
The current line chart falsely indicates that their are more values between the displayed point. But, for instance, if there were 10 visits on Monday and 20 visits on Tuesday, than you can't say that there were 15 visits in the night between both days or something.
I just investigated in how much work it would take to fix this bug. Fortunately, it can be done in seconds. We just need to change the $graphType to "bar" in line 21 of /core/ViewDataTable/GenerateGraphHTML/ChartEvolution.php
You can see a running demo here: http://piwik.vis4.net/
While I agree with the explanation, I find that the bar chart graph is more "heavy weight" in term of visual impact, I find there are too many dark pixels and it looks less nice.
Note: there is a small bug that the graph does not use 100% width.
At this stage I would prefer not to change but maybe there are ways we can make the bar chart looking nicer.... what are your thoughts?
Being able to switch between line and bar is actually implied by the current UI. A 'bar chart' icon is visible in the chart footer, while its hover text reads "vertical bar graph". Clicking on it just refreshes the line graph. This is a bug.
+1 to implement greg's idea in comment:5. Otherwise, simply remove the bar chart icon from the footer.