288 
MALARIA 
theless, the number of persons dying from 
malaria in the County is frequently much 
larger than in other counties where malaria 
death-rates are higher. 
In their simplest form, unit maps—the 
familiar “spot map”—show the actual 
number of cases or deaths either accurately 
located or expressed numerically in terms 
of political or other arbitrary subdivision, 
such as counties, parishes, or military dis¬ 
tricts. The difficulty with these maps is 
that certain subdivisions may be several 
times the size of others and so are not com¬ 
parable. This defect may be overcome by 
adjusting the attribute per subdivision to 
a constant unit area, as 100 square miles. 
This has been done in Fig. 4 with the data 
used in Fig. 3. It will be observed that the 
same general distribution of incidence and 
intensity is expressed in both maps, but 
that in the unit map, Fig. 4, the urban coun¬ 
ties—Fulton (Atlanta), Muscogee (Co¬ 
lumbus), Bibb (Macon), Richmond (Au¬ 
gusta), and Chatham (Savannah)—have 
greater prominence in the malaria picture. 
Thus it shows the aggregate effect of low 
exposure potentials in urban areas as well 
as the consequences of high endemicity in 
rural areas. The rate map emphasizes in¬ 
trinsic malariousness whereas the adjusted 
unit map depicts aggregate population ex¬ 
perience with malaria. Both types of maps 
are of value and should be made and stud¬ 
ied carefully to acquire a good understand¬ 
ing of the intensity-distribution of the 
disease. 
In the event that morbidity or mortality 
records over a suitable period of time are 
not available or are patently unreliable, the 
general picture of relative malaria inten¬ 
sity may be sketched in by making an area¬ 
wide malaria reconnaissance. This proce¬ 
dure is aimed at determining the current 
or recent prevalence of malaria in man. It 
is usually achieved by making a census of 
splenic enlargement or parasitemia, or 
both, among public school children through¬ 
out the area at any time during the year, 
though more useful data are obtained 
toward the end of the malaria season. 
These are plotted on a map to show their 
Fiq. 4 
