Tuesday 15 May 2012

Good Geographic Charting

I am not generally a fan of geographic mapping.  I have seen very few examples of it done well.

The problem is often the geography is not always directly proportional to the value being measured.  Take this example from The New York Times:

This is not an atypical image that one would see in this area.  A color is applied to each of the states to indicate a measure.  In this case, it is current Democrat (blue) versus Republican (red) support.

By the looks of this map, the republicans are doing very well.  But there is a distortion because many sparsely populated states and hence lower electoral college votes (e.g. Montana - 3, Wyoming - 3, Idaho - 4, South Dakota - 3, North Dakota - 3) have a large land mass.  On the other hand we have states with small land masses (e.g. New Jersey - 14, Massachusetts - 11, Maryland - 10, Connecticut - 7) that have much higher density populations and hence more electoral college votes.  Texas (38 votes) has a much bigger area than other states but it is actually California (55 votes) with the biggest vote.  Hawaii (4) is way smaller in area than Alaska (3), but it has one more vote.

The New York Times have actually taken a much better approach in their main Electoral Map.

This time they have changed the size of each state to represent the actual number of electoral college votes that they have.  Now, the map shows a much smaller swathe of red through the middle and more reflects the reality that (currently) the Democrats have a slight lead.

I really like this because it is a more accurate heat map while still retaining the geographic context.

I thought about how this might apply to Europe.  We are used to seeing a map like this (from Google Maps):

But the land area occupied by a country doesn't always reflect its population size.  I knocked-up this visualization in QlikView:

I haven't applied any color coding to this yet but it does give you an idea of how the populations are sitting.  For example, Sweden has a much bigger land area than Germany (about 450k km² versus about 360k) but has a much lower population (9.3m v 81.7m).  Iceland changes from a large island to a small speck in the ocean.

As with all charts, it is important to make sure that context is not skewed.  This method of geographic charting helps maintain the contexts.

Stephen Redmond is CTO of CapricornVentis a QlikView Elite Partner

1 comment:

  1. Hi

    Can you share the qvw file if any for this?



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