GIS for Mac OSX

Once, the only serious way to do much GIS work on your Mac was to use ArcGIS (or MapInfo) in a Windows virtual machine … but not anymore. QGIS Quantum GIS can now really compete with ArcGIS in terms of functionality and map creation. I miss a few things – proportional symbols for one – …

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QGIS on an Android tablet

Running QGIS on an android phone worked just fine – but running QGIS on an Android tablet is going to be a lot more useful, with a larger screen. I summarised the steps of installing QGIS on a Galaxy Advance (I9070) in a previous post, under Gingerbread (2.3.6); since then, there have been some issues …

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uTrack data to KML: parsing GPS data in Python

uTrack lets you download your vehicle GPS data as a CSV file. However, the CSV doesn’t include nicely-formatted lat/lon columns – instead, you get a fifth row with an address and latlon pair: Monduli,  (36.9005,-2.9013) My first attempt at a real Python script took me into regex, reading command line arguments, and basic CSV parsing, …

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Rotating a point grid in QGIS

Good ol’ GIS.stackexchange … I finally ended up posting a bounty of 50 reputation points for my rotation problem, and got an answer within a couple of hours! If you want to rotate a grid of points around (originX, originY) and degrees θ, enter the following values into the dialog (see image to the right): Scale …

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Spatial operations: R vs. spatialite

R and sqlite / spatialite have very different performance for the same spatial operation – in this example, an intersection. The example here is overlaying a point on a set of polygons and returning the data (census tract number). A quick R function that solved the problem (using US census tract data from TIGER): library(maps) …

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Spatialite and rasterlite on OSX

Spatialite and rasterlite are libraries for SQLite, a small database system that works from single files. SQLite databases are very easy to administer and share, and are read natively by QGIS without any need for configuring drivers and passwords! These two libraries let you add spatial capabilities to SQLite. If you’re already using QGIS (and …

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Using OpenStreetMap data in QGIS


OSM data for Arusha rendered in QGIS

One of the most commonly asked questions on the Tanzania GIS User’s group site is “where can I find good road data?” The data we had available generally 10 years ago was pretty poor – patchy and uneven coverage of the country, and poor metadata. OpenStreetMap.org now has a great deal of data available, contributed and edited by its users, and this can be used directly in QGIS.

 Click the image to the right to see an example … this is the OSM highway data downloaded as a shapefile from Cloudmade.com and rendered using the rule-based rendering for the layer.