If you've worked with ARC/INFO (or any GIS really), you often have to make a determination about the coordinate system of your data: if you want to reproject the data into another coordinate system, you use PROJECT , but if you want to simply overwrite the coordinate system of a layer, you would use DEFINE PROJECTION . PostGIS allows you to do both commands rather easily. So today, I'll show you both of them. I often find that I need to do these commands a lot, especially

Rather than starting with the easiest or hardest function, I thought I'd start somewhere in the middle - for GIS experts I don't want to bore you, and for novices, I don't want to blow you away with something more complex. But, after this post, we'll work through some easy queries and move on to more advanced queries. For those of you who used ARC/INFO, you probably found that the NEAR function was one of your best friends.  I used it every week to transfer attributes from

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