Visualizing results isn’t always the end goal of a spatial query. Often, someone just needs to write a report or provide a statistic. However, figures often help explain the data in a way that a report can’t, which is why mapping is such a useful tool for communication.
If you want to visualize the results of PostGIS queries, you have a few options. Depending on what software you use, the simplest method may be to export the data from PostGIS to another format, such as a GML file or an ESRI shapefile. Or you may want to view the data directly in a desktop viewer such as OpenEV or put it in a MapServer web map application.
You can use the
utility to convert from PostGIS into many other formats. As discussed
in Chapter 7, it is run from
the command line. Here is an example of how to convert the
mycounties view from PostGIS into a
shapefile, though any OGR-supported output format can be used:
ogr2ogr -f "ESRI Shapefile" mycounties.shp "PG:dbname=project1" mycounties
-f parameter specifies
what the output data format will be. The output dataset name will be
mycounties.shp. The source dataset
project1 database. The final
mycounties, is the name of
the layer to request from PostGIS. In this case it is a PostgreSQL
view, but it can also be a table.
The shapefile can then be loaded into any GIS or mapping product that supports shapefiles. This format is fairly ...