Lecture 2

The Basics, Part I

Here is animage from Information Anxiety, P286. This time the focus is on over designing the graphic. Trying to make the graphic 'exciting' makes it harder to get information from it. 

The purpose of visualization is to make it easy for the user to see the patterns, the similarities, the differences in the data. This involves both the variation in the data itself and the ability of a human being to perceive variation.

In general you do not want to let the computer use its default values. Unless you are using a specific program for a specific field the default values will not be right for your work. This is especially true of programs like Word and Excel (though both have improved a lot in the last couple years in this regard.)

Lets start with tables - the format of a table can greatly enhance or reduce the readability.

• Similar numeric data should have the same number of significant digits and be right justified - this makes it easier to see values getting bigger or smaller. Either use scientific notation, or don't, but dont mix scientific notation and standard notation. For big numbers in standard notation (e.g. 123482656) it can help to use commas to separate out the thousands, millions, billions places (e.g. 123,482,656).
  
  
• Row headings (especially those with multiple words) are easier to read if they are left justified
   
  
• Sans-serif fonts like Helvetica are easier to read on a computer screen than serif fonts like Times.
  
  
• If you have a table with just Yes / No values for every cell then only show the most appropriate one (eg 'Y') and leave the other one blank or ues a '-'. Its hard to scan a table with entries of Yes / No or Y / N quickly. Colour can also be helpful in highlighting the values you want the viewer to pay attention to.
  
  
• Have meaningful column headings and row labels. If you need multiple rows for the heading then break the words intelligently; dont let the program break up words where it feels like it.
  
  
• Tables should not cross a page boundary. If you have a really long table then replicate the column headings at the top of the next page/slide. A reader should not have to look to a previous page/slide to see what the column headings are
  
  
• If you have a big table it can be useful to alternate the background colour on adjacent rows with slightly different colours. This makes it easier to trace across a row.
  

Here is a table from the EPA - the Total Emissions column of data is centered making it very hard to compare the values within.

A better version of the table would be the following where both the sources and the amount of emissions are easier to see and quickly grasp:

Here is a made-up table - its hard to see any pattern in the Yes/No Values.

A better version of the table would be:

A different better version of the table using colour to help highlight the pattern would be:

Here is a table from the Nielsen Games page:
http://blog.nielsen.com/nielsenwire/media_entertainment/top-pc-game-titles-and-consoles-october-2008/

The rightmost column of numbers is hard to read because its left justified.

This version is easier to read because the right column of numbers is right justified. The decimal points line and bigger numbers look bigger.

Be careful of significant digits

Your table should not show more accuracy than the accuracy of the data collection. The computer will happily compute an average out to an alarming number of digits, but if you only took measurements to one decimal point then that's as far as you should show any derived (average, min, max, median, etc) values.

Programs may also reduce your significant digits by eliminating trailing zeros (turning 4.20 into 4.2) so you will want to force all the data of the same type collected in the same way to have the same number of significant digits.

For presentations, your tables should only show as much accuracy as needed to get your point across. If two values differ by 100 then you dont need to show those values to the third decimal place. The additional detail in the numbers gets in the way of seeing the bigger trend.

Here is another table from the same Nielsen page. Again left justifying the numbers makes things harder to read, but there are also an issueof significant digits. We can presume since they have been in the survey business a long time that they do have faith in their data out to that degree of significance, and very likely that number of digits is necessary to disambiguate data further down the table, but since they are just presenting the top 10, the extra digits get in the way.

I should point  out that if I was creating these tables myself then I would use white text on a black background, since these web pages have a black background

Simple charts

• Avoid 3D - really. 3D may make a chart 'exciting' but it also makes it much harder to see relationships. Drop shadows are ok if you really want a 3D look, but if in doubt you should remove any bling
  
  
• Avoid fully saturated colours (e.g. 255 0 0 red.) Look around you, most of the world is not bright primary colours. Pastels and colour mixtures are easier on the eyes (note the difference in Excel's colour default pallets at the bottom of these notes.)
  
  
• Choose an appropriate value for the axis to cross depending on what you want the user to see in the chart (e.g. should the smallest value be 0 which may minimize differences in the data, or closer to the low point in your dataset which will emphasize the differences in the data)
  
  
• The backdrop colour of the chart should match the backdrop of the page/slide you will put it on. For a paper the backdrop should be white. For the EVL powerpoint slide set the backdrop should be black
  
  
• If it is a line chart then make sure all the lines are visible against the backdrop. Do not accept the default colours (especailly if they are from pre-2007 Excel - those colours are terrible.) If certain lines are related to other lines then their colours should be related
  
  
• If it is a scatterplot of points then make sure the points are visible against the backdrop. If there is more than one point icon (eg circles and triangles, or red circles and blue circles) then make sure the viewer can see the difference from where they will be sitting. It can be very hard to see colour differences on small icons
  
  
• If you are labelling the data points, columns etc with their actual values (which is often a good idea) then make sure the text is readable against any lines in the background.
  
  
• Make sure all axis are well labelled in terms of what the axis is and the units / categories
  
  
• Make sure there is a meaningful title
  
  
• Make sure there is a legend explaining what the various lines / points / colours mean. The legend should be ordered in a logical way - eg if the lines / points / colours are based on a value like temperature then the legend should be ordered from low to high (or high to low depending on the field.) If the legend shows several independent things then the legend should be ordered in the same order as the general trend in the graph (ie things that are generally at the top of the graph should be at the top of the legend, things that are generally at the bottom of the graph should be at the bottom of the legend) to make it easier for the user to map between them.
  
  
• If certain data values relate to one another then they should be next to each other or have a similar color so its easier for the viewer to see the relationship
  
  
• If you have a series of graphs showing related results then try to keep the same axis extents, colours, patterns etc on all the charts
  
  
• It can be very important in certain fields to show error bars on your charts to show how accurate the measurements are
  

Here is an example charting the population of the USA over the last 8 years. First up is an overly dynamic 3D chart with a hard ro read set of population numbers and a trend that is made even more pronounced by the 3D viewpoint. Please do not create charts like this.

Here is a less exciting but ,uch more useful version where the data is shown in 2D and the population values have commas to make it easier to see what the numbers actually are. Another good possibility would be to make the vertical column "Population (in Millions)" and then have 270, 275, 280 etc as the vertical values.

Here are a couple variants using lines with the actual data points highlighted. The big difference is in the Y-axis. One chart suggests there is slow steady growth; the other suggests rapid steady growth.

and now lets go back to the video game console data from above.

First let's see a couple charts from the older version of Excel. The older Excel just wasnt very good at making charts - the colours hurt your eyes, the odd grey background shouldn't be there, etc. Its best just to avoid using the older Excel to make charts. It takes too much time to fix everything that is wrong.

The latest version of Excel is much better in dealing with colours and layout, but has also included lots of 3D bling that should be avoided. 3D distorts the data and adds in unnecessary details that makes it harder to see what's really going on. Please do not create charts like this.

Instead we can display the data without the 3D. By default Excel with pick the colours for the various data values as seen above. If the data values are unrelated then thats fine, but here we could also use the colour to relate consoles made by different , manufacturers (blue for Sony,  red for Nintendo,  green for Microsoft, and grey for Other, with the more saturated colours for their latest releases.)

It would be good if the colours you choose also work for people who are colour blind. You should at least make sure that you data doesnt blend together or disappear for people who are colour blind The colours I chose in the last couple graphs are OK, but an even better way is to avoid using green in your charts since red/geen is the most common form of colour blindness.  A good site to check your graphics is: http://colorfilter.wickline.org/

Coming Next Time

The Basics, Part II