I needed to find out all zip codes within VA senate and house districts. I obtained the zip codes from Fairfax County GIS data repository as a KML file. House and Senate maps were retrieved from the VA Redistricting Commission as shapefiles. These were added as Vector layers in QGIS. The Union operation (Layer>Geoprocessing>Union) was used to create a new layer with the merged data. Edit>Select>Select Features by Expression was then used to select Fields & Values>SENATEN = 35 for Sen. Saslaw’s 35th District, or any other district could be selected.