Wednesday, April 8, 2009

Color Blindness

6% of the male population cannot read the number 49 in this image:

but yet people use red and green to differetiate areas in Google Earth. Here's a screen shot from a well promoted Google Earth project that shall remain nameless to save blushes.

A long time ago I reported talking to a Googler who couldn't even see the borders in this view.

There are a few rules of thumb to help with avoiding color blindness problems in maps:
  • If you want to deliniate features using color, choose blends of yellow or blue, very few people have problems with identifying these colors.
  • Convert your colors to gray scales, if there is a tonal difference color blind users can still differentiate by tone.
  • Think of using different textures to mark areas. Unfortunately this isn't easy to do in Google Earth.
I'm doing some background reading at the moment and apparently color blindness is easily coped for by other features of our vision such as being able to recognise tone, texture, motion, focus. This means that color blind people often remain unaware they have a problem for years.


Paul C said...

Heh. Can't see a damn thing. Curse you, red-green band!

This is a critical issue and not just one which relates to colour use - this is one of a range of design problems which seriously affect usability. How much do you think these problems are a product of the lack of cartographic training in the neogeography community, and is there anything we can do about it?

Rich Treves said...


Good comment! Sorry you can't see the 49.

Yes, you're completely correct. Color blindness happens to be the easiest way to explain why cartography is still relevant. Neogeographers haven't been trained in it so we have a problem. As to how to solve it, I'll write a post...


Unknown said...

Here is a good lightweight cross-platform tool for testing to see how visual information might look to someone who is color blind:

Color Oracle