Five QGIS tips for Mac users
QGIS, a free, open-source data mapping application, has supported the Mac for years. But plugins are frequently developed on different platforms and introduce some wonkyness for those of us who like our computers fruit-flavored.
Here are five common problems and how to fix them:
Correct Mac install
Installing QGIS on a Mac can be a little complicated since it requires a few support programs to operate efficiently. Simply downloading the QGIS package that matches your operating system will work but QGIS will not function as well. Go to the Mac download page and download the GDAL and GSL frameworks and install them. You must have an admin password. Then download the QGIS package that matches your system and install it.
Field calculator doesn't work
QGIS is usually very forgiving of custom column headers but some tools have restrictions. They require that the headers have 10 characters or less, be letters or numbers and the only special character allowed is the underscore. You can edit your column headers in QGIS by installing the Table Manager plugin.
CSV doesn't import
Some plugins assume the user will try to import a Windows CSV. Macs output CSV files in a different format and sometimes the import fails. If you are working in Excel, select Save As… and choose Windows Comma Separated (.csv). That should fix many of the problems.
Boundary files with joined data won't display graduated color
There's a bug in QGIS 1.7 that causes the Equal Interval mode to fail when joining data to a boundary file via the new Joins tab in the Properties window. Once you have joined the data to the layer, right-click on the layer and select Save as… Select a projected coordinate system (UTM, etc.) and save it as a shape file. This merges the data to the shape file and once the new file is imported Equal Interval should display correctly.
Some ftools don't work:
Some of the functions in the ftools plugin will not work with on-the-fly projections. You can fix this by right-clicking on the layer you want to work with and selecting Save as… Save it as a SHP file and choose projected coordinate system (UTM, etc.) Re-import into QGIS and the tool should work.
QGIS is a free, open source GIS program that works on Mac, Windows and Linux. It's quite good for the price and is a great place to get started if you're interested in learning GIS mapping and analysis. You can learn more about the program in our QGIS basics for journalists tutorial.