Specifications

Map View more useful, such as
making the colors of the other layers
more intuitive (for example, blue
lakes) and thickening the lines desig-
nating the roads and rivers. I can
carry these out also with the Layer
Properties dialog (right-click on layer
name→Properties). A right-click on
the layer name also gives me the
option to change the layer name
displayed in the Legend.
Post-housekeeping, the Map View
in QGIS finally takes shape. I finally
can recognize features such as roads
and rivers, and now that the land-use
types are differentiated, I easily can
tell which areas are urban, agricultural,
forested and so on. Figure 3 shows
the end result.
To simplify visual analysis on my
map, I also applied the same color
to similar land-use categories. For
instance, I applied the same color to
two different agricultural categories
as well as three different forest-related
ones. For this application, I am inter-
ested to know only whether the land
use is agricultural or forested, not the
specific type of each. Fewer colors
makes my map less busy.
Navigating a Map in QGIS
Although QGIS contains several essen-
tial tools, I briefly discuss only three
here: the Pan, Zoom and Identify
Features tools.
The most essential tool for navi-
gating 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 unin-
tuitive 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 desig-
nated 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 fea-
ture, however, I must select the cor-
rect 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.
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 spe-
cific 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
INDEPTH
QGIS has versions for Mac OS X, Windows and
several variants for Linux users: source, Debian,
Ubuntu Gutsy and OpenSUSE.
90 | august 2008 www.linuxjournal.com
Figure 3. After modifying the properties of each layer and changing the layer names in the
Legend, the Map View is readable and ready for analysis.