A cartogram is a map, but a special type of map which attempts to convey a general sense of geography in addition to one or more other important statistical elements. Most maps attempt to portray an accurate image of the Earth’s surface, superimposed with other information such as political borders or place names. A cartogram, by contrast, is primarily concerned with accurately portraying a unique data set, while secondarily doing the best it can to stay true to geographic accuracy. 
Cartograms can visualize a wide range of types of information.
The following map is a gridded cartogram visualisation of global flight tracks taken from the OpenFlights database. The map distorts the land area by the number of flights that pass a certain space which leads to these ‘ploughing patterns’ over some areas where are airplanes basically just passing by, such as in the western part of Australia where planes simply fly over on their way to the most populated southeast of the country.
The colours in the map relate to the Worldmapper colour scheme. The colours used on the maps group the territories into 12 geographical regions, and allow for an easier visual comparison between the maps than would otherwise be possible. 
The colours of the world’s regions are chosen very consciously, and have a deeper sense behind their distribution. The world was split into twelve contiguous geographical regions of population groups, with every region being roughly symmetrically balanced and having at least a population of one hundred million people.The choice of which colour hue goes to which of the twelve regions of the world was made by looking at the Human Development Report. The HDR was used to sort these regions from the poorest to the richtest. Then, a rainbow colour scale was applied to determine the colour hue for each of the regions, starting with shades of dark red to demarcate the poorest territories, then moving through the rainbow scale to a shade violet for the best-off region which is Japan. 
This cartogram shows that a cartogram does not have to cover the entire world but can also span only a certain continent or country. Sources
 Victor Vescovo, (June 2006), The Atlas of World Statistics, What is a cartogram?
 Benjamin Hennig, (February 2016), Views of the World, Air Spaces: Where the Planes Fly.
 Benjamin Hennig, (February 2013), Views of the World, The Worldmapper Rainbow.
 Hennig, B. D. Ballas, D., and Dorling, D. (December 2015): In Focus: Europe’s uneven development. Political Insight 6 (3), 20-21.
The visualisation I came across this week is the following by Philip Hodges on his blog Zoho:Lab.
He made an interactive visualisation of NME‘s top album picks from 1974 to 2012 based on their genre.
His intention was to see whether the representation of genres (and hence their popularity) changed over the years. He used a circular bubble chart for his visualisation, in which the size of the bubble stands for the number of times a genre is associated with an album. How close the bubble finds itself to the middle, represents the weighting of the genre within the charts picks. Philip Hodges created a formula himself, but doesn’t share it in his explanations.
Bubble charts can be seen as a variation on the scatter plot, for data with two to four dimensions. The first two dimensions can be represented by x- and y-coordinates, a third by the size of the bubble and a fourth by the colour. Caution must be taken when deciding on the size of the bubbles. It is advised that you choose the radius relative to the square root of the corresponding data value, to avoid misleading representations.
I really like that this visualisation is interactive, as it allows you to play around with it. You can click on the genres to see the outline of one genre more clearly, and the surrounding visualisations are also updated when you do so. You can also hover over the bubbles and get a bit more information, wiki and amazon links are included,… I also think the visualisation makes it very clear which genre is more popular in a certain year, even if you don’t completely understand or know the weighting or the formula used.
My InfoVis of the week can be found at https://world.twingly.com/.
It is a real-time visualisation of the blogposts that are being published in the world. A geographical place gets a bar when a blogpost has been published. The more blogposts published from that place, the higher the bar will be. On the left of the screen, is a column with a live feed of all the titles of these blogposts. You can either hide or show this column. Every line is a link to that particular blogpost, so it takes you to the webpage when you click it. The pause button freezes the screen, in case you want some more time to go through the appearing titles.
While it is a fun visualisation, it it not very accurate. The sizes of the bars are hard to compare, both because the visualisation is in 3D and you can also not zoom in. Parts of the bars sometimes fall outside of the window as well.
It is however easy to see in which regions there are a lot of blogposts, which I think was the main purpose of this visualisation – even if you cannot pinpoint the exact city. The live feed is also a nice element, especially because it consists of clickable links. Overall, it looks like a very simple visualisation, and the purpose is immediately clear – in itself a big strength.