I know it's possible to make a trade area (service area) in ArcGIS. But Is it possible to make a trade area with a network data set in Grass GIS or QGIs?
GRASS GIS provides the
v.net.iso module which is equivalent to the trade area in ArcGIS. See the documentation and examples based on distance and travel time: http://grass.osgeo.org/grass70/manuals/v.net.iso.html