Those of us who work with maps on a daily basis struggle to get over to lay-users that not everything you will see on a screen, or in print, can be believed or trusted. Even though someone has gone to the time and trouble of creating a map there is a need to question everything; the underlying data, the method used, the way in which the results are presented, and the conclusions drawn.
Not everything you witness with your own eyes can be believed, your mind can play tricks. Take for example the ‘Checker shadow illusion‘ published by Edward H. Adelson, Professor of Vision Science at MIT in 1995 (image courtesy of butisit).
Here the squares labelled ‘A’ and ‘B’ are exactly the same shade of grey (yes really!), however, the mind distorts what the eyes see, and makes you believe that the square labelled ‘B’ is much lighter than ‘A’.
We recently worked with a client who were provided with some independent analysis of their business which showed that there were geographical areas where they were deficient in the service that they provided. When we appraised the analysis we found that some of the source data that they used could have been better (they didn’t look hard enough for a more granular data set), the methods used to generate catchments a little suspect, and the way that population distribution was measured at a micro level was not very accurate. All served to make the situation appear far worse for our client than it actually was.
Even the best in the world don’t always get it right. There is a blog article written by James Fee in 2009 which highlights a problem in Google maps where a long filled in lake is shown in an area of car parking and buildings. James did some detective work and traced the source to a forty year old United States Geological Survey (USGS) map which showed a lake which was part of a long defunct theme park. It looks like Google had used this as the source of their mapping.
So; seeing isn’t always believing.