How to Overlay Maps

In the video I tell the beginning of the story of how to overlay maps.  I’ll demonstrate one of the earliest examples of the strategic use of map overlay in planning. If you understand map overlay then you are a long way along the path to understanding GIS.

There are a few people in the history of geography who laid the foundations for the Geographical Information Systems that we have today. They developed the techniques and GIS is a tool that makes them more efficient. Map Overlay is important functionality in any GIS…that is the ability to overlay multiple maps onto each other so that new understanding of an area can be gained based on the relationship between the maps. A fellow called Ian McHarg deserves the most credit for the development of this technique. Although geographers at the time, poo-poo’d his techniques as being nothing new, because, of course, geographers had been overlaying maps forever, Ian McHarg was the first to consistently make the effort to pull all the information together in a way that they could be related to each other.

Ian McHarg wrote a book about this called “Design With Nature”. This is the least textbook-like of all the textbooks I have ever read. In fact, I’d go so far to say that contains prose moreso than text! McHarg’s story is one of a joyful childhood living equal distance from the city and country, the hideousness of WWII and his subsequent return to bulldozed memories. WWII left him with tuberculosis and his recovery from this began in a miserable dank filthy repatriation centre in Scotland, and ended with an opposing experience in a Swiss sanatorium surrounded by countryside and mountains. His experiences helped him see the link between health, happiness and environment, and he concludes that…

we need, not only a better view of man and nature, but a working method by which the least of us can ensure that the product of his works is not more despoliation (p.5)”


Ian McHarg, 1967, Design With Nature, John Wiley and Sons

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