[Sarah Battersby has on previous occasions shown how outrageously smart she is, but she has blown my mind today. I am sooo not worthy…]
I’ve been asked on occasion if we can show point data from one data source (containing explicit lat/lon fields) along with custom shapes drawn from a shapefile. My response in the past as been that you can if you convert the explicit lat/lon fields to a point shape so you can just change the GEOMETRY field on a dual axis map. The reason for this thinking was that I believed that you need to use the Latitude (generated) and Longitude (generated) fields for the GEOMETRY field and you couldn’t dual axis this with other lat/lon fields.
Well, it turns out I was wrong. I found this out when reading Sarah’s blog post about dual axis mapping (and specifically the section on combining a shapefile with a CSV):
There were two particular tricks she used in that section that caught my eye. First was the “faux union” done by a full outer join on the criteria of 1=0. What a neat trick – I’d never thought of doing that before! But the real winner was how she used the ZN(Latitude) and ZN(Longitude) to allow us to plot the GEOMETRY fields when the lat/lon values were NULL. I had no idea you could do that. Forest for the trees, or something like that…
Anyhow – the short of it is that I now know that it’s relatively easy to create a viz like this:
Thanks, Sarah! Genius!