The other day, I needed to draw a symmetrical object (a map point icon) in Inkscape, the wonderful free vector graphics editor. I was surprised to find that there is no symmetrical modeling feature, so I improvised. Here’s how to create a symmetrical polygon in…

Update 2011–12–14: It seems that a lot of people are coming here from web searches with phrases like “shapefile openlayers.” If all you want to do is display your data in OpenLayers, I’d highly recommend using a program like Quantum GIS to convert your Shapefile to a more web-friendly…

When you load GTFS data into PostGIS using gtfsdb, you can’t access that data in QGIS because the tables don’t have a primary key in int4 format (the primary key is in text format).

Over the last week I’ve started a new project, GTFSrDB, which allows you to connect GTFS-realtime with an SQL database, allowing app developers to use realtime data through SQL, just as easily as they use static data. Rather than worry about plumbing to connect GTFS…

Update 2011–11–12 8:21 -0800: I just posted a visualization I like better.

As a part of the Transit Appliance Project, I’ve been evaluating what transit agencies have real-time data; here’s a (non-exhaustive) list, focused primarily on U.S. agencies (note: these are…

Update 2012–02–02 17:57 -0800:I just wrote a post about another way to do this.

I really like QGIS. It’s a powerful GIS that runs on Linux (among other operating systems) and doesn’t require incredible amounts of CPU. One criticism I had of it was that it did not provide…

It seems that everyone who analyzes historical NextBus data has a different way of archiving their data. There are lots of ways one can use GIS to analyze this data, from creating movies showing the pulse of the transit system, to analyzing on-time performance…

I found this buried deep in an appendix of the Mapnik XML Schema Reference, and I thought it so useful I am reposting it here:

Zoom level Scale denominator

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