# Regions and size of an AGN

In this diagram of the regions and approximate scale of an AGN:

which is from this paper, what do the x and y scales log(z/pc) and log(r/pc) mean? I'm guessing z is the z-direction ('upwards') and r is radius, but what is the meaning of the pc bit?

pc is the abbreviation for parsec, a common unit of distance objects outside the Solar system. In order to compress the scales, they have also taken the logarithm (to base 10) of the distances in parsecs. So the scale in the figure on the x-axis in the radial (r) direction from the central black hole spans from 1e-5 to 100 parsecs. The z-axis, which is perpendicular or normal to the plane of the galaxy and the accretion disk, spans from 1e-5 to 1000 parsecs.