  Our knowledge of the environments of radio-loud AGN is still sketchy.
However, to understand the jet phenomenon it is important to know about the
properties of the surroundings in which jets are formed and evolve. Here I
present an analytical model of the radio surface brightness distribution of the
large scale structure of FRII-type radio sources. The `virtual maps' resulting
from this model can be compared with observed maps to obtain estimates for a
range of source properties from the model. These properties include parameters
describing the gas density distribution of the source environment, the energy
transport rate of the jets and the orientation angle of the source jet axis
with respect to the line of sight. The model is tested using radio maps of
Cygnus A for which there are independent measurements of some of these
parameters available in the literature. The model estimates agree well with
these observations. Varying the resolution of the radio maps used in
thecomparison does not change the results significantly.
