A visualisation is more effective than another visualisation if the information conveyed by one visualisation is more readily perceived than the information in the other visualisation.
With so many data presentation choices available, it is sometimes difficult to know which type of chart will show the information in the best possible format and maximise the understanding of the message contained in the data. It’s not always possible to say with certainty that one type of chart will work best for a given type of data being analysed.
Sometimes you just have to try different options and see what works best. It’s better to fail fast and recover quickly, rather than spend a lot of time on mastering a perfect design if that design doesn’t work to convey the message clearly.
There are several websites which can help with choosing a suitable chart .
- Graph Selection Matrix – presents your chart options in a walkthrough diagram
- Available chart types – provides a quick overview of charts available within Microsoft Excel 2013
- Nuts and Bolts & Graph Types (infographics) – provides a light hearted but informative summary of charts
The most commonly used and recommended charts are as follows:
Bar charts are especially effective when you want to compare data across categories. You can easily tell highs and lows at a glance. They can be used horizontally or vertically. Because the length of the bar is one of the attributes that encodes its quantitative value, its base should always begin at the value zero.
Dot plots can be a good alternative to bar charts. They offer additional advantages as they can be less cluttered, make it easier to include additional data and don’t require a zero value on the axis but still display a true data comparison.
Line charts connect individual numeric data points and as such a sequence of values. Their primary use is to display trends over a period of time.
Pie charts can be used to show relative proportions, or percentages of information. While still widely used by many, the experts agree that they are best avoided as they can be difficult to understand. This is due to the fact that our visual perception is not designed to accurately assign quantitative values to two dimensional areas. When the slices are of a similar size, it’s very difficult to know which one is bigger and by how much.
There are situations when pie charts can be useful, and if you use them, the advice is to limit the number of pie wedges to six. It helps if the sections are ordered according to the value they represent, from the biggest to smallest. Also make sure that the total percentage always adds up to 100%.
Information presented on maps can be great for any type of location data. You can use postcodes, regions or your own geocoding to show the geographical differences in your data.
If you are not quite sure what the data is telling you or whether different pieces of data relate, scatter diagrams can give you a sense of trends, concentrations and outliers.This type of diagram basically shows unaggregated data points for a variable. This presentation can help with further investigations and decisions about additional focus of the analysis.
Bubbles are a form of accentuated data on scatter plots or maps. Bubbles can add another meaning to the data by using colours and/or sizes, so that their impact is magnified.
You can use histograms to show how the data is distributed across categories or groups. The data needs to be divided into groups according to equal intervals, otherwise the number count in each category will not show a true picture.
Heat maps can be used when you are trying to compare data across two categories using different colour saturation. The darkest intersections can highlight most frequent categories. You can add another variable to the heat map by varying the size of squares.
A bullet graph is a modified version of a bar graph, developed by Steven Few to replace dashboard gauges and meters. It can be used to compare one or more measures (in this example student numbers against student targets). Its compact design is perfect for limited screen space, which is especially important when creating a dashboard. The background colours signify qualitative ranges, which can indicate the level of performance in this example expressed as 60 and 80 percent.