We have selected a sample of 55 kpc-sized flat spectrum radio sources from the JVAS/CLASS1 surveys which contain about 4800 objects. Optical (photometry and spectroscopy) and higher resolution radio follow ups are being carried out. Our sample is characterized by objects dominated by radio emission on kpc scales and splits, morphologically, into two: (i) 23 compact-medium symmetric objects (C-MSOs); (ii) 30 asymmetric core-plus-one-sided-jet (CJs) sources (half have sharply bent jets). Since the narrow-line emitting region (NLR) in active galactic nuclei (AGN) has a typical size of 0.1-1 kpc, both source types might be good probes of the structure and size of the NLR: by modeling, one can predict the observed shocks when a radio jet crosses the border of the NLR (density/pressure drop). Comparison with our actual observations will allow a geometrical estimate of the size of the NLR, if the jet is in the plane of the sky, the likely case for C-MSOs. For CJs, statistical and other techniques allow the determination of their orientation.