BOOKS OF RtfiDIfGS - PAHO/WHO

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REVEI.LE we believe to be the most uselul oí probleni stal;tmcnts for the pub:
E:' AL. lic f.cility prohlem. It i¡ a statementc thal adtnis tic multiplicity oí
locational objcctives and sccks those spatial pattirns that are superior
under a number of ,hese objectives.
'IThe purpose ol tiis article is to rcview thic location analysis literaturc
of the last fecw ycars that deals with public eiergency lfacilities.
Sorne of thisi literature represents studies directed toward specific
problems ol emcrgcncy medical services (EMS) systeras. primarily
location of ambulance dispatching points. Much of the lictrature.
lhowvecr. reports contex-free mode dels developed o atidlrcss location
probleiis imn general; these mnodels are not ticd to specilic applications.
Nevertheless, cach oí IIhe context-free miodels we shall discuss has
been applied in planning some forni of cmergency facilities. Wc
sh;lil trace iie develoipmient of thc coilteI .frcc moidcis inod .discuss
Iheir pieniaiil for furthier application iii emergency medical recovery
systciis. T'Ihere is an ad:d-tionial body oí location literature thait trals
locations on a plane, using ithe Euclidean metric; these works will not
he rcvicwed liere becalisc we feel that thc aippro:cil lacks rcalism fro
thie ypes of problems we wish o ; !dress.
Location-Allocation Models for EMS Systems
Ihe location-oriented literaturc Lth:t has ben developed in the
specific context of planmling emergency sysiems may e dlivided into
twu catcgories: thc first is coniLrtic n mainily with locationial and
sr!aial rcnsidcralions and occasionally inclides notions of randonm
.v,::? thiat are explored in an iecrative fa.slion throtugil simulation or
IqueCeing. Severnii o thlese works draw on the context-free location
literature. Thie secontd ci.tegory addresses thli event-service sequence,
with eniphasis on the random components o tlhe events. Location
anl. ', when it appears. is generally an ad Ihoc rather
integral leature oí thlese investigations.
ithan an
Spatial Analysia Applied to EIMS
Focusing on the average response timne. Vol¿ 3] applied a "steep.
est descent" procedure to eici,iiine locatiuois of ambulances. The
procedure, unlortunately, is subject to entrapinmet at local optinia.
Alhhouglt best soliations are possible, there is no way shiort of enu.
meration to verify whetiher a solution is inferior to the true optimum.
The model's suitability for planning ptirposes is hindered by its requiremnents
for data and computer time. Its complex structure makes
it very dillfcult to introduce other considerations and additional objectives.
The assumptiíon that emcrgenicy calls arrive as a Bernoulli
procesU (i. , with stationary independelnt inrcreients) may be unrealistic
in certain contexts. Volz added other assumptions thiat reduce
thie mathematical coniplexihy but impair themoldel's useuilness. NeviL^.LTkH
ertheles, thlis model was the fi st to trcal the interactiiou I>ctwcen
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