Quantum GIS: the Open-Source Geographic Information System

Exploring Quantum GIS (QGIS) using an example of real-estate planning.
Navigating a Map in QGIS

Although QGIS contains several essential tools, I briefly discuss only three here: the Pan, Zoom and Identify Features tools.

The most essential tool for navigating around a layer is the Pan tool, the toolbar icon in the shape of a hand. If I click on that tool, I quickly can drag my map around the Map View window.

However, if I want to change the level of detail in the Map View, I must switch to the Zoom tool. Although the Zoom tool is intuitive in function, beware, for it is disappointingly unintuitive in practice for three reasons. First, the Zoom tool resides in the View menu and is not available as a toolbar option. Second, the Zoom In and Zoom Out functions work only using the wheel of a mouse. Because I work on a laptop, I had to acquire a USB mouse just to have zooming capabilities. Third, unlike with most GIS and graphics applications, QGIS does not simply allow one to draw a box around the desired zoom-to area.

Meanwhile, the Identify Features tool is more straightforward and less cumbersome. To activate the tool, I simply press the toolbar icon designated by a mouse arrow next to the letter i in a blue circle. Then, I can navigate to any feature in the Map View window and essentially call up that feature's characteristics—that is, its entry in the attribute table. In order to select the appropriate feature, however, I must select the correct layer in the Legend. For example, if I am searching for information about a lake, I can't be on the Roads layer—the Lakes layer must be selected. Figure 4 shows how I clicked on a large lake and learned its size, elevation and name, Ford Lake.

Figure 4. The Identify Features tool gives you detailed information on a particular feature. Be sure you've chosen the right layer in the Legend.

Finding and Saving Ideal Locations

Now that I've covered the basics of GIS, found the requisite shapefiles, loaded those files into QGIS and explored basic navigation, it's time to find and record locations for my housing project. To find ideal sites where I can restore a wetland on agricultural land close to Ann Arbor, I pan and zoom around my map and toggle layers on and off.

After searching for a time, I decide to save some sites for later reference. The best way to do this is to create my own layer (shapefile). To do this, I click on the New Vector Layer icon in the toolbar, and because all I need are specific locations, I opt for a point-based shapefile. At the same time, I must build an attribute table, which I do by clicking on the Add Attribute button. I need only one string-based field, which I label Locations.

Now that I have my own shapefile, as long as that layer is selected in the Legend, I can add my own points to it by selecting the Toggle Editing tool. Once the tool is selected, the button right next door on the toolbar, the Capture Point tool, is activated, and I can create points anywhere I choose. I create a point for each potential building site I find and add a label to each, as prompted by QGIS. I press the Toggle Editing icon once again to leave edit mode and return to normal browse mode.

Thus far, QGIS has been useful in giving me a broad perspective on natural and man-made features, as well as land-use characteristics. This is much more than what nearly every paper map or Google Earth will give me. Still, QGIS can't do everything. Unfortunately, I probably can't acquire a shapefile with current land-ownership status. Therefore, I must utilize other resources, such as the County Clerk, in order to discover who owns which parcels. Clearly my work has only just begun.

Closing Words in QGIS

The free and open-source QGIS turns out to be an appropriate tool for projects involving land use, such as my search for a site to restore a wetland and build an eco-friendly housing development. In this project, I was able to locate the geospatial data I needed from a free geospatial data repository, load it into QGIS, tailor the data to my liking and designate a plethora of potential building sites. Besides land-use projects, you also can delve into demographic data, satellite and aerial-photo imagery, other natural and man-made features and more. Although cramming on GIS concepts and conventions was required, working with QGIS and other GIS applications, although a bit challenging at first, is extremely useful, rewarding and fun.


James Gray is Products Editor for Linux Journal

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