Resumen
We introduce a new method to analyze proper motion data. The method is called ``criss-cross'' mapping. It emphasizes regions where proper motion vector extensions cross or converge. From a superposition of lines through the vectors, a map is generated which helps to interpret the kinematic data. The new mapping technique is applied to the young planetary nebula BD+30 3639. The data are approx. 200 internal proper motion measurements from Li, Harrington, & Borkowski (2002). From the criss-cross mapping of BD+30 3639, we conclude that the kinematic center is approximately 0.5 arcsec off-set to the South-East from the central star. The mapping also shows evidence for a non-homologous expansion of the nebula that is consistent with a disturbance aligned with the bipolar molecular bullets.
