Two of my favorite things: my trusty ARC/INFO mug from 1990, and my trusty dog Pepper, painted in the style of Andrew Wyeth's Homer . At the recent FOSS4gNA conference , I had the pleasure of hearing about some of the new features in PostGIS. One such set of features were the Coverage related features ( ST_CoverageInvalidEdges , ST_CoverageUnion , ST_CoverageSimplif y ). These functions made certain adjustments in the data structure to allow for faster spatial operations. L

I don't think ARC/INFO ever had the ability to create a bivariate map. The first time I saw it, it was implemented in ArcMap. There are also cool looking bivariate maps produced with ArcOnline . ESRI also has a .dll you can use, and there is a good article here . So of course that got me thinking: could we make the same map with PostGIS? Well, sure, and it is super easy. If you want to get spun up on what these 9 color bivariate choropleth maps are, and the theory be

As promised, I'm going to expand on the BUFFER example and talk about the Multi-Ring Buffer . I felt it was too much to go over in one blog post, so we'll cover it now. The Esri help manual has a nice diagram for the buffer operation: Returning to the set of points we've been using: a multi-ring buffer would be as follows: This one is a little tricky because we don't want the concentric circles to overlap one another. So, if we are buffering by 0.5, 1.0, and 1.5 then we ha

Another ARC/INFO function that we often use is DISSOLVE . This is an easy one, as PostGIS has the command ST_Union. An example from the Esri manual shows how counties in Iowa are dissolved: But I'm going to use an example of counties in the Northeast United States: The query to do this is simply: This is simply performing a Union operation on the geometry field, and then grouping that union on a field name. You can group by multiple names, or even make other conditions. T