Quantum GIS Basics - Desktop GIS: Mapping the Planet with Open Source Tools - page 323

Systems, on page 138 for details). Using the Change button, you can
set the projection for the layer.

Usually QGIS sets the parameters you see here based on the projection
information associated with the layer. If there is no projection infor-
mation, then QGIS makes an assumption based on your preference
setting for projections. You can set QGIS to do the following when a
layer is loaded that has no projection information:

• Prompt for projection
• Use the projectwide default projection as set in the Project

Properties
• Use the global default projection specified in your user preferences

If you want to take a look at these options now, open the Preferences
dialog box, and click the Projection tab.

Subset
The last piece of the General tab concerns itself with the subset of the
data. This feature lets you create a subset of your layer on the fly and
display only the data matching the criteria you specify. Currently this
works only with PostGIS layers. For an example of how to use this
feature, take a look at Section 7.4 , Using PostGIS and Quantum GIS, on
page 110 .

Metadata Tab
The Metadata tab provides detailed information about the layer, includ-
ing its location, type, number of features, and projection. In Figure D.1 ,
on the next page, we can see the Metadata tab contents for our world_
borders layer.

The General information provided shows us not only information about
the layers physical location but also the type—in this case an ESRI
shapefile. We can also see that our layer contains polygon features and
has a number of editing capabilities. Well, these aren't really capabil-
ities of the layer but show you what QGIS can do with the layer in
terms of editing. With the world_borders layer, we see that we can add
and delete features, create a spatial index, and change the values for
attributes in the layer. This is useful information, especially in the case
where you just downloaded a new layer and it's still a mystery to you.

The metadata also includes information about the extent of the layer. It
shows the extent in both the coordinate system (spatial reference sys-
tem) of the layer and the project. You might notice that they are the