Filtering a layer by attributes

In addition to the spatial queries outlined in the previous recipe, we can also subset a layer by its attributes. This type of query resembles a more traditional relational database query and in fact uses SQL statements. In this recipe, we will filter a point shapefile-based layer by an attribute.

Getting ready

We'll use the same New York City Museums layer used in the previous recipes in this chapter. You can download the layer from https://geospatialpython.googlecode.com/svn/NYC_MUSEUMS_GEO.zip.

Unzip that file and place the shapefile's contents in a directory named nyc within your qgis_data directory, within your root or home directory.

How to do it...

In this recipe, we'll filter the layer by an attribute, select the filtered features, and zoom to them, as follows:

1. First, we load the point layer:

   lyrPts = QgsVectorLayer("/qgis_data/nyc/NYC_MUSEUMS_GEO.shp", "Museums", "ogr")
   

2. Next, we add the layer to the map in order to visualize the points:

   QgsMapLayerRegistry...