Getting the Most Out of QGIS and GRASS Integration - Desktop GIS: Mapping the Planet with Open Source Tools - page 200

required parameters for the tool on the Options tab; then when the tool
is run, the output shows up on the Output tab. Clicking the Manual
tab displays the manual page for the GRASS tool you are working with.

The Options tab contains a drop-down box populated with the layers
eligible for conversion. In this case, since we have only world_mosaic.tif
loaded, it's the only thing in the list. To convert it, we just need to
supply a name for the output map. Rather than be original, we'll use
world_mosaic for the output name. Now all that's left to do is click the
Run button and watch the output fly by. Once the raster is imported,
we can review the contents of the Output tab to look for any prob-
lems or see the results and details of the conversion. Not only that,
but it also provides a good way to learn about what's going on inside
GRASS. Assuming all went well, we now have the world_mosaic loaded
in to GRASS. Load it up in QGIS using the Add GRASS raster layer tool.

Those are the basics of getting data into GRASS using the import capa-
bilities of the toolbox. Notice that not only can we load an OGR vec-
tor layer, but we can load PostGIS as well. Sometimes it makes sense
to convert your data, and other times you can just use them in their
native form in QGIS with your GRASS data. If you need to manipulate
the data, it's best to bring it into GRASS.

Once you've added a GRASS map to the map canvas, it works pretty
much like any other layer in QGIS. You can identify features, make
selections, view the attribute table, and label features. The one thing
you can't do is edit the data—at least not through the editing tools
we've seen thus far in QGIS.

12.2 Editing GRASS Data with QGIS

Editing vector GRASS maps in QGIS is also done via the GRASS plug-
in. The editing tools are designed to work with the underlying GRASS
vector model, which is different from a shapefile or PostGIS data store.
GRASS is topological, meaning it understands the relationship between
adjacent features and stores common boundaries only once. Shapefiles
and PostGIS data, on the other hand, are nontopological—each feature
is stored in its entirety, with no regard for adjacent features.

To be able to edit a GRASS map, you obviously need to have the mapset
open and the map loaded into QGIS. You may think I'm stating the
obvious here, but in fact you can load a GRASS map without opening
the mapset. If you do that, the toolbox, region tools, and editing tool