Knots, hot spots, and boundaries of radio sources are regarded as the interface of jets with their surroundings in a discussion of several recently found morphological associations between extended radio emission and optical emission lines. These line/radio associations are seen in both radio and Seyfert galaxies, usually just outside bright radio regions and close to bends in the radio sources. Two radio galaxies with extended associations are considered: 3C305, and Coma A (3C277.3), which is remarkable for the strong similarity of its H-alpha emission map to the radio morphology. Several interpretations of the measured velocities in the extranuclear emission line gas, dependent on the origin of the gas, are discussed. In conclusion, it is proposed that broad-line regions may be intimately associated with the parsec-scale flat spectrum radio cores.