Quantum GIS

Quantum GIS (QGIS) is a user friendly Open Source Geographic Information System (GIS) that runs on Linux, Unix, Mac OSX, and Windows. QGIS supports vector, raster, and database formats. QGIS is licensed under the GNU General Public License. QGIS lets you browse and create map data on your computer. It supports many common spatial data formats (e.g. ESRI ShapeFile, geotiff). QGIS supports plugins to do things like display tracks from your GPS. QGIS is Open Source software and its free of cost (download here). We welcome contributions from our user community in the form of code contributions, bug fixes, bug reports, contributed documentation, advocacy and supporting other users on our mailing lists and forums. Financial contributions are also welcome.

Newsflash

Quantum GIS Version 0.11.0 has been released. It is available in source form, and as binary executables for Microsoft Windows, Mac OS X, and GNU/Linux. All versions can be obtained from our download page. If the version for your platform is not available please check back in a day or two as some packages are still being built.

No Labels on Your PostGIS Layers?

If you are experiencing problems labeling data from PostGIS, the likely cause is your layer lacks a spatial index. The symptoms of this problem are simple: all your features are labeled with the default text chosen from the layer properties dialog. This typically means all your features are labeled with the word: Label. All PostGIS layers should have a spatial index to improve performance when zooming in or displaying the data at less than full extent. You also need the index to perform spatial queries (see the PostGIS Manual for details).

Checking for Missing Indexes
You can check which layers are missing a spatial index using the following query from psql:

select f_table_name from geometry_columns where f_table_name not in (select tablename from pg_indexes where indexdef ilike '%using gist%' and tablename = geometry_columns.f_table_name and schemaname = geometry_columns.f_table_schema);

This will give you a list of tables that lack a spatial index.

Creating a Spatial Index
To create a spatial (GiST) index, use the following syntax:

CREATE INDEX [indexname] ON [tablename] USING GIST ( [geometryfield] GIST_GEOMETRY_OPS );

After creating the index, you should force PostgreSQL to collect statistics using VACUUM ANALYZE. See Section 4.5 of the PostGIS manual for details on creating a spatial index.

Example
CREATE INDEX sidx_lakes_5k ON lakes5000 USING GIST ( the_geom GIST_GEOMETRY_OPS );

Note, creating a GiST index can take a long time depending on the number of rows in the table.

Future QGIS Enhancements
In the future, QGIS will warn you when adding a PostGIS layer that lacks a spatial index. In addition, the SPIT plugin will be enhanced to optionally create the index when you import a shapefile.