  The objective of the cover location models is covering demand by facilities
within a given distance. The gradual (or partial) cover replaces abrupt drop
from full cover to no cover by defining gradual decline in cover. In this paper
we use a recently proposed rule for calculating the joint cover of a demand
point by several facilities termed "directional gradual cover". Contrary to all
gradual cover models, the joint cover depends on the facilities' directions. In
order to calculate the joint cover, existing models apply the partial cover by
each facility disregarding their direction. We develop a genetic algorithm to
solve the facilities location problem and also solve the problem for facilities
that can be located anywhere in the plane. The proposed modifications were
extensively tested on a case study of covering Orange County, California.
