Quantum GIS: the Open-Source Geographic Information System
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.
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.
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.
Practical Task Scheduling Deployment
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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- The Firebird Project's Firebird Relational Database
- Stunnel Security for Oracle
- My +1 Sword of Productivity
- SUSE LLC's SUSE Manager
- Managing Linux Using Puppet
- Non-Linux FOSS: Caffeine!
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- Google's SwiftShader Released
- Parsing an RSS News Feed with a Bash Script
- Doing for User Space What We Did for Kernel Space
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide