Spatial Query Plugin

The spatialQuery Spatial Query Plugin allows you to make a spatial query (i.e., select features) in a target layer with reference to another layer. The functionality is based on the GEOS library and depends on the selected source feature layer.

Possible operators are:

  • Contains
  • Equals
  • Overlap
  • Crosses
  • Intersects
  • Is disjoint
  • Touches
  • Within

Using the plugin

As an example, we want to find regions in the Alaska dataset that contain airports. The following steps are necessary:

  1. Start QGIS and load the vector layers regions.shp and airports.shp.
  2. Load the Spatial Query plugin in the Plugin Manager (see The Plugins Dialog) and click on the spatialQuery Spatial Query icon, which appears in the QGIS toolbar menu. The plugin dialog appears.
  3. Select the layer regions as the source layer and airports as the reference feature layer.
  4. Select ‘Contains’ as the operator and click [Apply].

Now you get a list of feature IDs from the query and you have several options, as shown in figure_spatial_query_1.

  • Click on selectSubsetLayer Create layer with list of items.
  • Select an ID from the list and click on selectCreateLayer Create layer with selected.
  • Select ‘Remove from current selection’ in the field And use the result to selectString.
  • You can checkbox Zoom to item or display checkbox Log messages.
  • Additionally in Result Feature ID’s with the options ‘Invalid source’ and ‘Invalid reference’ you can have a look at features with geometry errors. These features aren’t used for the query.

Figure Spatial Query 1:

../../../_images/spatial_query_sample.png

Spatial Query analysis - regions contain airports