Quantum GIS (qGIS) for the Mac

A while back I reviewed MyWorldGIS, indicating my disappointment with the analysis capabilities of other available free or low-cost GIS for the Mac. Well, no longer. Since its birth in 2002, Quantum GIS (qGIS) has grown to be an impressively powerful application in its own right.

qGIS is an Open Source Geographic Information System (GIS) licensed under the GNU General Public License. QGIS is an official project of the Open Source Geospatial Foundation (OSGeo) and is a volunteer driven project. It runs on Linux, Unix, Mac OSX, and Windows and supports numerous vector, raster, and database formats and functionalities. In this review I’ve chosen to highlight its Mac-ness, both because I am a Mac user and I am often asked about Mac GIS options.

Over its life-cycle, qGIS has dished out a continously growing number of capabilities provided by core functions and plugins – and appears to be still growing strong. You can visualize, manage, edit, analyze data, and compose printable maps. Best of all (in my opinion) is a robust set of vector data analysis, geoprocessing, geometry, and data management tools and functionality now available. Sometimes open-source software gets a bad wrap for being too complicated, particularly in the graphical user interface (GUI) department. It is what it is – made by techies for techies, qGIS is a growing powerhouse of geospatial tools, though it might not win GUI awards for simplicity. Did I mention it is also free?

Overview of qGIS Features

First let’s get acquainted. A summary of features include:

1. View and overlay vector and raster data in different formats (including GIS shapefiles) and projections without conversion to an internal or common format.

2. Create maps and interactively explore spatial data, including on the fly projection, spatial bookmarks, identify/select features, feature labeling, change vector and raster symbology, and more.

3. Create, edit and export spatial data, including GPS tools to import and export GPX format, convert other GPS formats to GPX, or down/upload directly to a GPS unit.

4. Perform spatial analysis using the fTools plugin for Shapefiles.

5. Publish your map on the internet using the export to Mapfile capability (requires a webserver with UMN MapServer installed)

These Are a Few of My Favorite Things

As a disclaimer, I typically use qGIS to explore shapefile data, manipulate data, and save selections of shapefiles to prepare them for import into our Ortelius cartography software (to which I am affiliated). My review is clearly influenced by these uses and by the questions we get from our own users wanting to do more with GIS.

qGIS Stand-Alone Installation

On the downside (or upside – depending on your point of view), there are a lot of download options. First, there are separate downloads for each operating system. Each also has a variety of dependancy frameworks with their own requirements. The standalone Qgis does not include GRASS support at all, if you want it you must use the standard Qgis package + frameworks + GRASS if you need GRASS features (GRASS is a GIS used for geospatial data management and analysis, image processing, graphics/map production, spatial modelling, and visualization – it is not required for qGIS though can provide added functionality). Wowza. This might leave many potential casual users puzzled before they even have the software!

Have no fear – a stand-alone installation ‘all in one’ bundle for Mac OS X is provided for “new users.” In fact, I highly recommend it for all but very technically-minded and advanced users.

Analysis With fTools qGIS Plugin

Do you need to count the points of one layer in polygons of another layer? Select by location? Buffer or intersect features? Convert feature geometry?Join attributes with an external table? Or more? If so, you definitely need analysis tools. Choose Plugins > Manage Plugins… from the main menu and enable the fTools plugin for data management and analysis. Doing so will add “Vector” to the main menu and provide a variety of tools for manipulating your vector GIS data.

I am often asked about software to join external spreadsheet data with GIS data. To do this, you need a common data field, such as country name, in both data sets. Choose Vector > Data Management Tools > Join Attributes from the main menu to identify your target GIS layer, join field, and database file to join. Note that you cannot directly link to Pages® or Excel® spreadsheets, rather you must link to a DBF file. This is especially a pain since Excel (Mac 2008) stopped having a DBF export option. I have turned to using open-source software NeoOffice to convert my spreadsheet data to DBF to prepare for linking attribute tables. It is an inconvenient step, so if you have a better solution for Mac users, please share! Once you’re done, the automatic save of the output shapefile makes things especially easy.

X,Y Data to Shapefile

Lots of people have X,Y coordinate data (e.g., latitude/longitude data) in spreadsheet format that they want to display on a map. In fact, if you have a simple address list, you can use a service such as BatchGeocode.com to generate your X,Y data for you, then use the results to create shapefiles in qGIS. First choose Plugins > Manage Plugins… from the main menu and enable the Add Delimited Text Layer plugin. In the main menu, the Plugins menu will now list “Delimited Text” among its options. Use the GUI to import your tab delimited X,Y data.

Vector Editing

qGIS supports editing the points, lines and polygons of shapefile map data. Choose Layer > Toggle Editing to activate the editing toolbar. qGIS has a suite of editing tools to cut and add features.

Save Selection as Shapefile

Perhaps I use this most – I simply love the easy of which you can select features in a layer and save them as a new shapefile. Use the Select Features tool from the toolbar to directly select features on your map, or open Attribute Table and select features from the table view. Then, simply choose Layer > Save Selection As Shapefile form the main menu. It’s as easy as that and a powerful tool when pairing down large shapefiles to your area of interest.

Conclusion

While there are a plethora other features that could be mentioned, these are among the ones I use the most. On the down-side, the cartographic rendering in qGIS is typical of a low- to mid-range GIS programs (unfortunately which can easily produce ugly GIS-looking maps). Although packed with features, the program can be overwhelming for new users who are just getting started with GIS. If you are in that lot, the provided Users Manuals are required reading. I find the GUI a bit cluttered with buttons, such as the five different buttons for importing a layer when one might suffice. Organization in the GUI might also be improved by consistently locating active plugins – either by adding active plugins to the Plugin menu or as separate menu items, but not both – it can  be confusing when you activate a plugin and it isn’t where you expect it to be.

Overall, qGIS is a strong performer with a dedicated volunteer development base. Kudos to the development team for continuing development on this much needed application. It gets high marks in analysis and data management and I recommend it for Mac GIS users.

There are unlimited uses of GIS software in general, and qGIS specifically, that I haven’t covered. Do you have experience with qGIS you’d like to share? Do you have experience with other GIS for Mac tools? If so, I’d love to hear from you.