| Summary: | The concept of "primacy" as introduced by Jefferson
in 1939 in urban geography leads to the notion of
"dominant city" also known as the primate city. Practically,
the notion was extended by Sheppard in view of discussing
some "hierarchy". The type of dominance is not
universal nor any hierarchy reversal. Both can be time and
sample dependent. Thus, as an example taking into consideration
the existence of both pieces of the puzzle, we
consider and discuss the Bulgarian urban system. It is also
interesting to compare data on two groups of cities in different
time intervals: (i) the whole Bulgaria city system
which contains about 250 cities, - studied in the time interval
between 2004 and 2011, and (ii) a system of 33 cities,
- studied over the time interval 1887 till 2010. These latter
cities are selected because the population was already
over 10 000 inhabitants in 1946. It is shown that new
additional indices are interestingly introduced in order to
compensate defects in the Sheppard index. Numerical illustrations
are illuminated through a "length ratio" measure,
which allows to distinguish the (often) observed departures
from the hyperbolic ranking seen by Jefferson.
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