Please use sensible colours in your maps

November 2, 2011

(This article was first published on Robin's BlogRobin's Blog » R, and kindly contributed to R-bloggers)

If you are creating maps then for goodness sake

Use sensible colours! 

I was helping some undergraduates with some work the other day, and they decided to use the following colour scheme for representing river depth:

  • Deep water: Red
  • Medium-depth water: Bright green
  • Shallow water: Pink
Why did they do this? Well, either they were the default values used by the software they were using (unlikely), or they just chose randomly. Not a good idea.
If you look you’ll find a huge amount of literature about this (I should put some references here but I can’t really be bothered at this time at night), and it really makes your maps a HUGE amount more useable if you’re using sensible colours. For example:
  • Deep water: Dark blue
  • Medium-depth water: Medium-blue
  • Shallow water: Light blue
Why is this sensible? Well it makes sense on a number of levels – water is normally shown as blue (so it’s obviously some kind of water), and the different levels of colour imply some sort of ordering. With the original colours above there is no inherent ordering – is green ‘higher’ or ‘lower’ than red? Of course, red and green being used for ‘incorrect’ and ‘correct’ on a different map would be very sensible…

Isn’t it hard work to come up with nice colour schemes for all of your maps? Nope not at all – ColorBrewer has done it already! If you haven’t used this website already I urge you to do so, it provides a number of carefully-chosen colour-schemes designed for various different purposes. For representing river depth you’d probably want to use one of the blue Sequential schemes, but there are also Diverging schemes for data that goes off in two directions, as well as schemes for representing Qualitative data (those that have no explicit ordering). What’s more you can tell it to only show schemes that are color-blind-friendly, photocopier-safe etc, and it’ll produce a preview for you with various map styles (labels, cities, coastlines etc). All in all it’s very impressive, and very useful.

Plugins and extensions are available for a number of pieces of software to allow ColorBrewer colours to be easily used. These include an ArcGIS plugin (see the bottom answer for how to install with ArcGIS 10), R package, Python module and IDL routines.

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