Surveyor General's Office, 1889, Sydney
Approx. 28" x 25"

Scanned in four sections and assembled in Photoshop. More information can be found here: http://catalogue.nla.gov.au/Record/1906378

Note the elegant method of tying the amount of rain at a given location to the diameter of the red circle. The key in the lower left demonstrates this relationship, providing rain levels at specific increments. However, far from being encouraged to take out a compass and test specific circles, one's instinct is to absorb the composition as a whole: The coast is quite literally saturated, while further inland we find much less red ink.

An interesting thought, then, is this: If the measuring stations were for some reason more concentrated inland and less so at the coast, the overall feel of the graphic would be drastically changed, appearing more evenly colored or even more saturated inland than on the coast. It's certainly curious that we find the dots relatively free of overlap. One wonders what decisions were made, if any, regarding what data to omit, in order to make the overall impression more effective.

View a larger image here.