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V  Cutini  &  V  Di  Pinto

 

On  the  slopes  of  Vesuvius:  Configuration  as  a  thread  between  hazard  and  opportunity

 

 

66:1  

066

On  the  slopes  of  Vesuvius:  

 

Configuration  as  a  thread  between  hazard  and  opportunity  

Valerio  Cutini  

University  of  Pisa   valerio.cutini@unipi.it  

 

Valerio  Di  Pinto  

University  of  Naples  Federico  II   valerio.dipinto@unina.it  

Abstract  

This  paper  focuses  on  the  urban  agglomeration  that  has  gone  growing  up  along  the  centuries  on  the   western  side  of  Vesuvius,  a  still  active  and  fearsome  volcano,  few  kilometres  southeast  from  Naples.   In   view   of   the   dimension   of   the   agglomeration   and   of   the   spontaneous   and   unplanned   way   it   has   been   growing,   the   purpose   is   to   investigate   on   the   actual   role   Vesuvius   –   as   an   element   of   both   danger  and  richness  –  has  gone  assuming  in  the  urban  self-­‐organization.  This  paper  will  analyse  the   grid   configuration   of   the   whole   settlement,   in   order   to   discuss   the   way   Mount   Vesuvius   has   been   interiorized  (if  it  actually  has  been)  in  the  spatial  choices  and  behaviour  of  the  local  communities  so   as  to  benefit  from  its  presence  and  to  co-­‐exist  with  its  threat.  Three  major  results  are  expected  from   the   findings:   to   examine   and   verify   the   actual   resilience   of   the   whole   agglomeration,   so   as   to   evaluate   the   extent   to   which   the   concern   and   alarm   are   actually   justified;   to   analyse   the   configurational  state  of  the  system  in  order  to  pinpoint  possible  actions  for  risk  mitigation;  more  in   general,  and  aside  from  the  case  of  the  Vesuvius  area,  to  evaluate  how  risk  from  natural  hazard  is   spontaneously  mitigated  in  self-­‐organized  urban  spaces;  and  if  self-­‐organized  urban  structures,  when   exposed  to  natural  hazards,  really  work  better  than  we  may  think  or  fear.  

Keywords  

Hazard,  grid  configuration,  resilience,  self-­‐organization.  

   

“Above  these  places  lies  Mt.  Vesuvius,  which,  save  for  its  summit,  has  dwellings  all  round,  on   farm-­‐lands  that  are  absolutely  beautiful.  As  for  the  summit,  a  considerable  part  of  it  is  flat,  but   all  of  it  is  unfruitful,  and  looks  ash-­‐coloured,  and  it  shows  pore-­‐like  cavities  in  masses  of  rock   that  are  soot-­‐coloured  on  the  surface,  these  masses  of  rock  looking  as  though  they  had  been   eaten  out  by  fire;  and  hence  one  might  infer  that  in  earlier  times  this  district  was  on  fire  and  had   craters   of   fire,   and   then,   because   the   fuel   gave   out,   was   quenched.   Perhaps,   too,   this   is   the   cause  of  the  fruitfulness  of  the  country  all  round  the  mountain  (…)  And  the  whole  of  the  gulf  is   garnished,  in  part  by  the  cities  which  I  have  just  mentioned,  and  in  part  by  the  residences  and   plantations,   which,   since   they   intervene   in   unbroken   succession,   present   the   appearance   of   a   single  city.”  

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V  Cutini  &  V  Di  Pinto

 

On  the  slopes  of  Vesuvius:  Configuration  as  a  thread  between  hazard  and  opportunity

 

 

66:2     “This  is  Vesuvius,  until  recently  green  with  wine  leaves  where  the  celebrated  grapes  filled  the   wet   vats.   These   mountains   Bacchus   preferred   more   than   the   hills   of   his   native   Nysa,   this   is   where   the   satyrs   performed   their   dances.   Here   was   the   city   of   Venus   [Pompeii]   that   she   preferred  over  Sparta,  and  the  city  that  was  named  after  the  glory  of  Hercules  [Herculaneum].   Now  everything  is  abeyantly  buried  from  flames  and  gloomy  ash:  even  the  gods  would  not  have   permitted  such  a  destruction.”  

M.  Valerius  Martialis,  Epigrammata,  book  IV.  ep.  44(A.D.  87)    

1.  Introduction  

The  slopes  of  Vesuvius,  on  the  western  side  of  the  volcano,  are  home  to  one  of  the  most  problematic   urban   areas   all   over   Europe,   frequently   mentioned   and   discussed   with   concern   and   serious   alarm   (among  others,  Barnes,  2011).  More  than  one  million  people  presently  live  in  the  direct  shadow  of   Vesuvius,   within   a   wide   agglomeration   that   has   gone   growing   spontaneously   along   the   centuries,   without  (and  against)  any  territorial  plan  or  policy,  under  the  threat  of  a  still  active  and  fearsome   volcano:  its  last  eruption  dates  back  to  1944  but  a  forthcoming  catastrophic  event  is  presently  feared   and  even  expected,  so  that  scares  keep  periodically  coming  up,  evoking  the  dreadful  memory  of  the   ancient  tragedy  occurred  in  A.D.  79.  

Mount   Vesuvius   has   a   long   eruptive   history,   which   has   been   continuing   for   over   400,000   years,   periodically  peaking  in  major  eruptions  alternated  with  moderate  energy  events  according  to  a  cycle   of  about  20  years.  The  last  greatest  eruptions  were  in  1631  (more  than  7,000  victims),  1760,  1794,   1834,  1861,  1872,  1906  (the  most  violent  event  in  the  twentieth  century)  and  1944  (the  last  great   event,   spewing   out   more   than   70   million   cubic   metres   of   lava).   Such   a   regular   and   frequent   occurrence   is   therefore   easily   expected   to   have   deposited   into   the   historical   memory   of   the   local   communities   a   deep   ancestral   fear   of   the   volcano   as   well   as   a   full   awareness   of   the   deadly   risks   coming   from   it.   Yet,   as   the   settlements   have   recently   gone   spontaneously   growing   despite   that   hazard,  it  may  be  presumed  that  such  fear  and  awareness  could  not  but  have  somehow  oriented  the   form  and  the  structure  of  the  settlement,  in  order  to  safeguard  it  and  to  enhance  its  resilience.   Nonetheless,  it  ought  to  be  noticed  that  Mount  Vesuvius  is  not  only  an  undisputed  source  of  danger   for   the   million   inhabitants   of   its   slopes.   The   volcanic   ash   and   lapilli   erupted   from   the   craters   and   spread   around   along   the   ages   have   strongly   fertilized   its   slopes,   making   that   land   outstandingly   fruitful  and  an  ideal  breeding  ground  for  an  amount  of  local  crops,  such  as  special  local  varieties  of   tomatoes,   apples,   apricots   and   grapes.   Furthermore,   exceptionally   favourable   microclimatic   conditions   make   the   western   slope   of   Mount   Vesuvius   a   highly   desirable   location   for   residence,   which  can  also  benefit  from  a  unique  view  of  the  entire  gulf,  from  Naples  to  Capri  and  Sorrento.     Summing  all  up,  what  makes  this  wide  context  one  of  the  most  dangerous  areas  of  the  world,  under   terrific,  permanent  and  not  eliminable  threat,  is  just  what  also  makes  it  one  of  the  richest  and  most   attractive   agricultural   lands   all   over   Italy,   source   of   wealth   and   employment   as   well   as   a   strong   element  of  cultural  identity.  

The   acknowledged   presence   of   volcanic   risk   suggested   in   2001   to   encompass   a   wide   area   around   Vesuvius,   called   ‘red   zone’,   including   the   18   municipalities   where,   in   case   of   violent   eruption,   a   complete  destruction  is  predicted  and  ought  to  be  expected.  Around  the  red  zone,  an  orange  zone,  a   yellow  zone  and  a  green  one  were  defined,  including  progressively  lower  risk  areas.  In  2013  the  red   zone   was   extended   up   to   its   present   consistency,   which   includes   27   municipalities,   around   350   sq.km,  with  a  population  over  1,100,000  inhabitants.  For  some  time  now,  there  is  full  awareness  of   the  terrific  risk  looming  over  the  whole  area;  since  1995  the  Italian  department  of  Civil  Protection   has  developed  a  National  Emergency  Plan  for  the  evacuation  of  all  the  red  zone  residents  in  case  of   eruption,   providing   to   move   out   the   refugees   by   different   transport   modes   and   predetermined   routes,  so  as  to  distribute  them  in  18  Italian  regions,  from  Piedmont  to  Sicily.  In  the  present  paper  

(3)

V  Cutini  &  V  Di  Pinto

 

On  the  slopes  of  Vesuvius:  Configuration  as  a  thread  between  hazard  and  opportunity

 

 

66:3   the  attention  will  be  focused  on  the  most  exposed  portion  of  this  red  zone,  the  coastal  strip  lying   between  the  western  slopes  of  Vesuvius  and  the  seaside  and  bounded  on  the  north  by  the  southern   edge  of  Naples  and  on  the  south  by  the  northern  edge  of  the  Sorrento  peninsula,  covering  an  area  of   about  120  sq.km  (Fig.  1):  9  municipalities,  including  Pompeii  and  Herculaneum,  and  a  population  of   380,000  inhabitants  (tab.  1).  

  Figure  1:  The  observed  area,  superimposed  to  a  3D  view  of  the  Vesuvian  coast  

 

The  whole  area  is  completely  urbanized,  as  a  result  of  the  rapid  development  of  the  various  ancient   nuclei   in   the   second   post-­‐war   period,   so   as   to   presently   appear   a   unique   wide   conglomeration   sprawled  over  the  western  slopes  of  Mount  Vesuvius.  

 

Municipality   area  (km2)   Population   population  density  of  

(inhabitants/km2)  

Portici   4.52   60,218   13,322  

Ercolano   19.64   56,738   2,889  

Torre  del  Greco   30.66   90,608   2,955  

Trecase   6.14   9,179   1,495   Bosco  Trecase   7.49   10,638   1,420   Bosco  Reale   11.20   27,618   2,466   Torre  Annunziata   7.33   48,013   6,550   Pompei   12.41   25,751   2,075   Scafati   19   50.275   2,646   TOTAL   118.39   379.038   3,202    

Table  1:  Municipalities  within  the  observed  area  

 

The   commonly   discussed   matter   obviously   concerns   the   way   of   clearing   out   the   whole   area,   resettling   its   inhabitants   on   a   safer   urban   place   –   hard   task   to   achieve,   for   economic   and   social   reasons   –,   or   the   management   of   an   emergency   evacuation   plan   –   challenging   too,   due   to   the   breadth  of  the  area  (a  rough  rectangle,  20  km  long  and  7  km  wide),  its  administrative  fragmentation   and   its   population   density   (3,202   inhabitants/km2,   with   a   peak   of   13,322   in   the   municipality   of   Portici,  among  the  highest  in  Europe).  

 Far   from   neglecting   such   aspects   and   overlooking   the   actual   problems,   this   research   will   look   elsewhere,   focusing   on   the   spatial   configuration   of   the   area.   Since   its   particular   geographic  

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V  Cutini  &  V  Di  Pinto

 

On  the  slopes  of  Vesuvius:  Configuration  as  a  thread  between  hazard  and  opportunity

 

 

66:4   conditions,  tightened  between  the  crater  and  the  seaside,  have  undoubtedly  strongly  influenced  the   urban  structure  and  its  development  down  the  centuries,  this  paper  aims  at  investigating  the  actual   role  Vesuvius  –  as  an  element  of  both  danger  and  richness  –  has  gone  assuming  in  the  urban  self-­‐ organization.  In  other  words,  this  paper  will  discuss  if  mount  Vesuvius  has  been  taken  into  account  in   the  spatial  choices  and  behaviour  of  the  local  communities  so  as  to  determine  the  development  of   urban  spaces  compatible  with  the  volcano,  in  order  to  benefit  from  its  presence  and  to  co-­‐exist  with   its  permanent  threat.  The  thesis  is  that  the  presence  of  the  volcano  and  the  effects  it  induces  on  the   surrounding   urban   area   are   somehow   internalized   within   the   configurational   properties   of   its   grid   and  can  therefore  be  investigated  and  made  to  emerge  by  means  of  space  syntax  techniques.     The   area   appears   covered   with   a   continuous   urbanization,   as   a   consequence   of   the   demographic   growth  of  the  pre-­‐existent  urban  nuclei;  among  them,  the  most  important  and  densely  populated   centres  are  (running  from  north  to  south)  Ercolano,  Torre  del  Greco,  Torre  Annunziata  and  Pompei.   The  resulting  conurbation  currently  occupies  the  whole  area  on  the  western  side  of  Vesuvius  with  a   low  density  urban  structure,  interstitial  with  respect  to  the  more  densely  built  areas  of  the  ancient   nuclei.   The   theme   of   its   adjacency   to   the   hazards   and   opportunities   of   mount   Vesuvius   appears   therefore   flanked   by   the   theme   of   its   recent   development   as   a   conurbation,   overlapping   and   replacing  the  pre-­‐existing  cities.    Space  syntax  will  hence  be  applied  to  analyse  both  those  issues,  so   as  to  answer  the  crucial  question  regarding  the  capability  of  this  special  conurbation,  thanks  to  its   spatial  configuration,  to  deal  with  the  hazards  and  opportunities  mount  Vesuvius  actually  provides.   In  the  observed  case  study,  the  grid  configuration  appears  suitable  to  describe  the  way  the  Vesuvian   conurbation   fits   the   specific   condition   and   the   geographic   context   of   its   site,   so   as   to   exploit   the   territorial  opportunities  it  provides  and  to  cope  with  the  hazards  it  presents.  In  other  words,  such   issue  concerns  the  way,  if  any,  the  local  communities  materialize  the  fear  from  natural  hazards  and   the  attraction  towards  territorial  opportunities,  developing  and  adapting  their  settlements  in  order   to   prevent   themselves   from   the   former   and   to   take   benefit   from   the   latter;   in   other   words,   it   concerns   the   way,   if   any,   the   fear   from   natural   hazards   and   the   attraction   towards   territorial   opportunities   are   actually   internalized   within   the   structure   of   the   settlement,   so   that   they   can   be   made   to   emerge   by   mean   of   space   syntax   techniques.   Furthermore,   aside   from   the   case   of   the   Vesuvius   area,   the   same   findings   are   expected   to   indicate   if   actually   risk   from   natural   hazard   is   spontaneously  mitigated  in  self-­‐organized  urban  spaces,  and  if  self-­‐organized  urban  structures,  when   exposed  to  natural  hazards,  really  work  better  than  we  may  think  or  fear.  

2.  Backgrounds  

As  it  was  shown  above,  two  wide  issues  appear  crisscrossing  under  the  singular  case  of  the  Vesuvius   area.  On  the  one  hand,  setting  aside  the  threatening  presence  of  the  volcano,  this  case  evokes  the   general  issue  of  the  genesis  of  a  conurbation  from  the  development  of  several  pre-­‐existing  nuclei,   which  have  gone  growing  and  mutually  merging  so  as  to  form  a  radically  different  urban  settlement,   provided  with  a  new  and  different  inner  geography.  Such  issue  can  be  suitably  investigated  by  space   syntax   techniques,   so   as   to   point   out   the   transformation   the   configurational   state   of   each   single   system  undergoes,  as  it  progressively  grows,  merges  to  the  others  and  concurs  in  forming  a  greater   global   system.   And   it   can   be   easily   observed   that   the   inner   geography   of   the   conurbation   -­‐   when   deriving  from  the  growth  of  cities  of  similar  size  –  deprives  its  original  nuclei  of  their  own  centrality,   which  is  addressed  towards  the  connection  fabric  between  them.  The  configurational  effects  of  the   genesis   of   a   conurbation   are   clearly   exemplified   by   the   case   of   the   making   of   the   Versilian   conurbation,   along   the   northern   Tuscany   seaside,   developed   in   the   twentieth   century   as   a   consequence  of  the  growth  of  the  three  main  nuclei  of  Viareggio,  Marina  di  Pietrasanta  and  Forte   dei   Marmi.   The   image   in   figure   2   represents   the   configurational   state   of   the   Versilian   system   (represented  by  the  distribution  of  global  integration  value)  at  three  dates  -­‐  1939,  1954  and  2004  -­‐,   so  as  to  reproduce  its  diachronic  dynamics.  

The  image  above  points  out  the  radical  change  the  inner  geography  of  the  settlements  undergoes  as   they  go  merging:    their  integration  core  appears  migrating  from  the  respective  original  cores  towards   the   long   seafront   street   that   represents   their   main   mutual   connection;   this   configurational   state   actually   corresponds   to   the   distribution   of   urban   centrality,   as   it   is   represented   by   the   density   of  

(5)

V  Cutini  &  V  Di  Pinto

 

On  the  slopes  of  Vesuvius:  Configuration  as  a  thread  between  hazard  and  opportunity

 

 

66:5   movement   and   activities.   In   such   geography,   the   original   urban   nuclei   of   Viareggio,   Marina   di   Pietrasanta   and   Forte   dei   Marmi   appear   to   remain   the   repository   of   a   merely   local   centrality,   confirmed  by  the  distribution  of  radius  3  integration  value.  

   

Figure  2:  The  diachronic  genesis  of  the  Versilian  conurbation.  Distribution  of  global  integration    

The   second   issue,   specifically   related   to   the   observed   case   study,   is   the   close   proximity   of   this   conurbation  with  an  acknowledged  and  permanent  source  of  great  risk,  what  Vesuvius  undoubtedly   is.  When  it  goes  at  discussing  the  behaviour  of  an  urban  settlement  in  front  of  a  natural  disaster  like   a  volcanic  eruption,  we  enter  the  wide  -­‐  and  widely  discussed  -­‐  theme  of  urban  resilience.  Several   declinations   of   such   theme   have   been   so   far   provided,   aimed   at   reproducing   different   features:   resilience   has   been   from   time   to   time   appraised   and   regarded   as   the   possibility   of   the   territorial   organization   to   rescue   e   make   safe   the   affected   population   (Gil   and   Steinbach,   2008;   Muhareb,   2009;  2011),  the  capability  of  the  urban  settlement  to  retain  the  efficient  working  of  its  plants  and   infrastructures  (Jha  et  al.,  2013),  the  steadiness  of  its  social  wholeness  and  cohesiveness  (Paton  and   Johnston,  2006;  Pelling,  2003;  Cutter  et  al.,  2003),  the  ability  of  quickly  recovering  after  a  disaster   (Carpenter,  2012)  or  the  capability  of  an  urban  system,  thanks  to  its  own  spatial  features,  to  adsorb   destructions  and  transformations  without  significantly  changing  its  inner  geography  (Cutini,  2013),   and  so  on.  What  significantly  links  all  these  issues  (and  several  others  not  mentioned  above)  is  the   reference   to   some   impending   (natural   or   artificial)   hazard   that   cannot   be   avoided   as   well   as   the   purpose  of  adsorbing  it  and  going  ahead,  hanging  over  it  despite  the  destructions  it  may  cause.  On   such  issues,  space  syntax  has  already  played  its  part,  discussing  the  role  of  the  grid  configuration  on   vulnerability  to  disasters  and  suggested  the  use  of  configurational  indices  for  a  variety  of  purposes:   in  order  to  reproduce  the  level  of  resilience  with  reference  to  the  seismic  risk  (Sari  and  Kubat,  2011);   to  point  out  the  spatial  factors  that  provide  the  capacity  of  rebounding  after  a  disaster  (Carpenter,   2012;  Carpenter,  2013),  adsorbing  the  impact  of  change  on  inhabitancy  and  cultural  identity  (Koch   and  Carranza,  2013),  or  spreading  risk,  creating  buffers  and  facilitating  reorganization  (Marcus  and   Colding,  2014);  to  investigate  on  the  spatial  features  that  can  assure  the  capability  of  sustaining  local   alterations   of   the   grid   with   limited   changes   on   its   global   behaviour,   what   was   called   network   resilience   (Cutini,   2013).   Although   all   these   notions   could   be   usefully   applied   in   any   situation   concerned  with  the  threat  of  disasters,  in  the  present  paper  the  network  resilience  will  be  taken  into   account,  as  a  suitable  tool  for  evaluating  the  efficiency  of  the  streets  network  and  its  performance  in   the  immediate  post-­‐perturbation  phase,  also  with  reference  to  urban  accessibility  and  evacuation.   As   this   notion   appraises   resilience   as   a   matter   of   diffused   richness   in   alternative   paths   from   any   origin  to  any  destination,  three  main  indices  have  been  so  far  introduced  and  tested,  and  they  will  be   applied  in  the  observed  case  study.  

(6)

V  Cutini  &  V  Di  Pinto

 

On  the  slopes  of  Vesuvius:  Configuration  as  a  thread  between  hazard  and  opportunity

 

 

66:6   A   first,   basic   parameter   is   the   mean   connectivity   value   of   the   grid,   which   roughly   reproduces   the   density  and  variety  of  paths  connecting  each  line  to  all  the  others  of  the  axial  map.  Low  values  of   connectivity  are  expected  standing  for  the  frequent  presence  of  obliged  paths,  while  on  the  contrary   high   mean   values,   in   case   of   paths   interruption,   are   likely   to   guarantee   a   dense   presence   of   alternative  paths.  Its  value  varies  from  2  to  n,  thus  reproducing  the  capability  of  the  urban  system  to   absorb   a   material   grid   transformation   without   significantly   modifying   its   relational   state:   in   other   words,  its  capability  to  adapt  its  movement  pattern  to  different  spatial  layouts.  The  roughness  of  this   index   derives   from   the   fact   that   it   merely   depends   on   the   number   of   connections,   but   is   not   influenced  by  their  spatial  distribution.  

A   further   index   of   network   resilience   takes   into   account   the   distribution   of   shortest   paths:   being   resilient  the  systems  that  are  provided  with  a  widespread  presence  of  shortest  paths  all  over  the  grid   and,  on  the  contrary,  vulnerable  those  that  are  characterized  by  their  dense  concentration  through  a   small  number  of  spatial  elements.  On  such  basis,  an  indicator  of  resilience  was  introduced  (Cutini,   2013)  as  the  ratio  of  the  highest  choice  value  and  the  maximum  frequency  a  line  could  present,  what   would  occur  if  it  were  located  on  all  the  shortest  paths  between  any  couple  of  the  other  lines.  If  we   consider  an  axial  map  of  n  lines,  it  was  shown  that  this  index,  to  be  called  frequency  index,  is    

v  =  choicemax  /  (n2/2  –  3/2  n  +  1)  

The  frequency  value  varies  from  0  to  1,  increasing  as  the  resilience  of  the  system  decreases.  Should  a   line  be  located  on  all  the  shortest  paths  connecting  all  the  couples  of  lines  (v  =  1),  the  system  would   result  vulnerable  to  its  highest  degree,  in  that  each  of  its  paths  will  share  (and  depend  on)  that  single   line.  The  idea  that  urban  resilience  somehow  depends  on  the  capacity  of  the  whole  system  to  take   and   adsorb   local   perturbations   suggested   to   introduce   a   further   configurational   parameter,   reproducing   the   strength   of   the   correlation   between   the   distribution   of   integration   values   at   different   scales   (local   versus   global).   Since   integration   was   proved   suitable   for   reproducing   the   distribution  of  urban  centrality  at  different  values  of  radius,  a  narrow  correspondence  of  global  and   local   integration   can   be   assumed   as   a   clue   of   steadiness   of   the   system:   any   perturbation   will   be   expected   not   to   upset   the   local   distribution   of   accessibility,   as   strongly   anchored   to   its   global   pattern.   In   other   words,   the   R2   coefficient   of   the   correlation   radius   3   versus   radius   n   integration   (called  synergy  coefficient)  appears  suitable  for  indicating  resilience  or  vulnerability.  Such  parameter   and   the   two   presented   above,   taken   together,   can   hence   be   used   as   tangible   indicators   of   the   resilience  of  the  whole  system.  

  Figure  3:  The  analysed  Vesuvian  conurbation    

(7)

V  Cutini  &  V  Di  Pinto

 

On  the  slopes  of  Vesuvius:  Configuration  as  a  thread  between  hazard  and  opportunity

 

 

66:7  

3.  Grid  configuration  and  resilience    

The   construction   of   the   Vesuvian   urban   system,   because   of   the   unavailability   of   a   reliable   and   updated   numerical   cartography,   has   been   manually   drawn   exploiting   the   official   national   imagery   (Fig.  3).  The  process  has  been  made  in  GIS  environment,  working  on  the  WMS  service  provided  by   the  Italian  national  cartography  portal  (pcn.minambiente.it).  

The  resulting  set  of  public  spaces  has  been  modelled  into  depthmapX  software  (Varoudis,  2012),  to   be   analysed   by   a   configurational   approach.   The   same   software   was   used   to   process   the   map   by   angular   segment   analysis,   assuming   Tulip   analysis   at   1024   bins,   and   metric   and   segment   step,   respectively,  as  analysis  type  and  radius  type.  

The   discussion   of   the   results   can   exploit   the   space   syntax   capability   to   construe   multi-­‐scalarity   in   urban   grids.   At   the   global   scale   (fig   4),   the   distribution   of   configurational   values   shows   that   the   integration  core,  that  is  the  set  of  lines  with  higher  values  of  integration,  retraces  the  main  axis  road   that   crosses   the   whole   urban   system,   while   the   integration   values   follow   a   decay   trend   as   the   distance   increases.     The   distribution   of   choice   value   is   similar,   but   characterized   by   a   much   more   emphasised  peak  on  the  main  road  axis.    

  Figure   4:  Distribution  of  global  integration  (above)  and  global  choice  (below)   -­‐  Colours  vary  from  red  (higher  

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V  Cutini  &  V  Di  Pinto

 

On  the  slopes  of  Vesuvius:  Configuration  as  a  thread  between  hazard  and  opportunity

 

 

66:8   At  a  local  scale,  the  distribution  of  radius  3  integration  (Fig  5)  clearly  highlights  the  historical  original   nuclei,  as  well  as  their  weld  joint  along  the  main  road  axis.  The  development  process  based  on  this   mechanism   of   merging   is   better   shown   by   the   comparison   of   local   choice   distribution   at   different   metric  radii  (Fig  6).    

  Figure  5:  Distribution  of  local  integration  -­‐  topological  radius  R3  (depthmap  std.  colour  ramp)  

 

  Figure  6:  Distribution  of  local  choice  at  different  metric  radii  (depthmap  std.  colour  ramp)  

 

Summing  up,  the  analysis  of  the  urban  grid  shows  how  dependent  the  whole  system  is  on  a  set  of   few  lines;  and  such  result  can  only  be  strongly  related  to  the  conurbation  genesis  process,  that  is  the   welding  of  standalone  urban  nuclei  along  a  main  road  axis  crossing  the  whole  area.  

(9)

V  Cutini  &  V  Di  Pinto

 

On  the  slopes  of  Vesuvius:  Configuration  as  a  thread  between  hazard  and  opportunity

 

 

66:9   In   order   to   evaluate   the   syntactic   resilience   of   the   whole   system,   the   indexes   above   have   been   calculated  with  reference  to  the  entire  conurbation,  without  any  fragmentation  into  sub-­‐elements.   Each  computation  has  been  carried  out  basing  on  the  result  of  angular  segment  analysis,  assuming  a   topological  radius  3.  The  numerical  output  is  reported  below  (tab.  2).  

 

Mean  Connectivity   Synergy   Frequency  Coefficient  

4.62   0.169   0.396  

Angular  Segment  Analysis  –  T1024  –  Topological  Radius    

Table  2:  Resilience  Indexes  calculated  on  the  Vesuvian  conurbation  system  

 

Discussing  the  meaning  of  those  results  without  any  endogenous  basis  for  comparison  is  a  difficult   issue.  None  of  those  indexes,  in  fact,  was  so  far  clearly  classified  in  literature  and,  moreover,  they  are   probably  still  underdeveloped  (Conroy  Dalton,  2010).  However,  referring  to  other  available  findings,   mean   connectivity   and   frequency   (Cutini,   2013)   values   appear   perfectly   consistent   with   what   the   distribution   of   choice   and   integration,   both   at   global   and   local   scale,   let   us   foresee:   a   poorly   connected   network   (as   shown   by   a   low   value   of   mean   connectivity),   with   a   high   concentration   of   geodesic   paths.   Moreover,   the   poor   value   of   synergy   coefficient   clearly   means   a   weak   correspondence   between   local   and   global   scale,   thus   standing   -­‐   as   discussed   above   -­‐   for   poor   resilience.  

Going   deeper   into   the   problem   of   the   resilience   of   the   Vesuvian   conurbation,   the   relationship   between  resilience  and  risk  needs  to  be  pointed  out,  requiring  some  further  consideration  on  the   notion  of  resilience,  which  in  urban  studies,  as  hinted  above,  is  not  unequivocally  defined  (Esposito   and  Di  Pinto,  2014).  In  order  to  clear  out  any  ambiguity,  in  general  we  should  assume  that  there  is   not  a  ‘resilience’  if  not  related  to  a  well  defined  urban  phenomenon  to  which  a  “perturbation”  of  the   system  is  to  be  referred  to;  what  involves  that,  in  general  terms,  there  are  so  many  ‘resiliencies’  as   urban  phenomena.  Despite  the  configuration  of  the  urban  grid  is  not  a  phenomenon  in  itself,  but  the   common  language  of  the  space  that  influences  urban  phenomena  (Hillier,  1999),  yet  it  is  movement   what  shapes  this  influence,  as  the  very  interface  between  the  grid  configuration  and  the  phenomena   along  its  paths;  what  was  strongly  pointed  out  defining  the  grid  as  a  mechanism  for  ‘maximising  the   randomness  of  encounter  through  spatial  proximity  and  movement’  and  thus  cities  as  ‘movement   economies’  (Hillier,  1996).  It  is  therefore  movement  what  also  substantiates  the  notion  of  network   resilience,  mentioned  above  and  appraised  as  an  intrinsic  property  of  the  urban  grid.  Such  a  meaning   can  here  be  enriched  by  the  reference  to  the  presence  of  an  actual  risk.  In  general  terms,  the  risk  is   constituted  by  two  components:  the  magnitude  of  a  potential  loss,  and  the  probability  that  the  loss   will  occur.  Strategies  for  risk  management  may  therefore  point  to  reduce  the  loss  or  to  lower  the   probability  that  it  will  occur.  If  attention  is  focused  on  the  loss,  it  can  be  understood  as  the  result  of   the   overlap   between   a   perturbation   induced   by   an   exogenous   factor   and   the   endogenous   reorganization   of   a   system.   Configuration   analysis   is   highly   suitable   for   looking   into   both   those   aspects  with  an  integrated  approach,  through  the  evaluation  of  the  indexes  of  permeability  before   and   after   the   event.   In   addition,   the   configurational   analysis   can   even   do   more   and   better:   it   can   assess  the  potential  of  a  system  to  reorganize  after  a  change,  regardless  of  the  nature  and  location   of  the  perturbation.  Moreover,  thanks  to  this  feature,  it  is  also  possible  to  assess  the  resilience  of   any  urban  phenomena  dependent  on  space  configuration:  what  actually  completes  and  extend  the   notion   of   network   resilience.   Having   taken   that   into   account,   when   it   comes   to   the   object   of   the   present  study,  a  deeper  and  more  area-­‐oriented  analysis  can  hence  be  performed.  In  particular,  a   heavy   spatial   impedance   appears   to   affect   movement   towards   the   boundary   of   the   conurbation:   what   is   likely   to   involve   dramatic   problems   if   a   catastrophic   event   should   occur,   thus   suggesting   discussion  on  possible  risk  mitigation.  

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V  Cutini  &  V  Di  Pinto

 

On  the  slopes  of  Vesuvius:  Configuration  as  a  thread  between  hazard  and  opportunity

 

 

66:10  

4.  Configuration  and  risk  mitigation  

In   order   to   evaluate   the   resilience   as   an   endogenous   property   of   the   urban   network,   the   configurational   indexes   introduced   above   are   to   be   interpreted.   The   mean   connectivity   value,   roughly  reproducing  the  density  and  variety  of  paths  within  the  grid,  can  be  read  as  an  indicator  of   connection   redundancy   to/from   each   point.   In   case   of   perturbation,   the   higher   the   mean   connectivity,   the   smaller   the   isolation   of   any   point   in   the   network   is   likely   to   be.   The   synergy   coefficient,   measuring   how   much   the   local   street   system   is   a   reliable   predictor   of   global   configuration   (Conroy   Dalton,   2010),   actually   expresses   the   average   impedance   that   local   pattern   represents  when  moving  from  any  point  to  the  main  elements  of  the  network,  and  generally  from   the   edge   towards   the   centre.   In   case   of   perturbation,   the   greater   the   synergy,   the   lower   the   impedance  (in  terms  of  topological  steps)  to  reach  the  main  structure  of  the  system  will  be  expected.   The   frequency   coefficient   (Cutini,   2013)   actually   concerns   movement:   it   expresses   the   degree   of   concentration  of  shortest  paths  within  the  grid.  In  case  of  an  event,  the  higher  its  value,  the  smaller   the  probability  of  being  near  a  high  choice  line  will  result;  or,  in  other  terms,  more  difficult  moving   toward  the  grid  boundary  will  be.  Moreover,  the  interruption  of  few  high  choice  lines  could  easily   upset  the  movement  pattern  all  over  the  grid,  or  even  undermine  and  jeopardize  the  whole  system,   making   it   not   entirely   connected.   In   order   to   capitalize   on   the   use   of   those   indexes,   it   is   worth   introducing   endogenous   references.   Besides   the   present   grid   consistency   of   the   settlement,   two   additional   scenarios   have   been   generated   and   analysed.   A   diachronic   scenario   is   aimed   at   understanding  how  the  dynamics  of  the  settlements  has  gone  influencing  the  change  in  resilience.   The  second,  referred  to  the  current  situation,  is  then  aimed  at  understanding  if  the  infrastructures   for   non-­‐local   movement   do   actually   play   a   role   with   respect   to   the   system   resilience.   The   first   scenario  (SC_1957)  describes  the  system  at  1957.  The  second  (SC_2015_MWY)  describes  the  system   at  2015,  but  supplements  it  with  the  motorway  A3  that  crosses  it  (Fig.  7).    

   

Figure  7:  Segment  maps  of  SC_2015_MWY  (on  the  left)  and  SC_1957  (on  the  right)    

The   resilience   coefficients   were   calculated   with   reference   to   the   three   scenarios,   and   their   comparison   (tab.   3)   highlights   the   features   of   the   settlement   dynamics,   characterized   by   the   transition  from  a  linear  system  of  urban  nuclei  to  an  uninterrupted  coastal  conurbation.  The  actual   increase  in  synergy  values  between  1957  (SC_1957)  and  2015  (SC_2015;  SC_2015_MWY)  appears  a   consequence  of  the  transition  from  a  series  of  related  parts  (high  synergy  within  each  nucleus  and   low  synergy  of  their  whole  set)  to  a  uniform  urban  system  (higher  synergy  value  within  the  whole   settlement).   On   the   other   hand,   the   significant   decrease   of   mean   connectivity   expresses   in   configurational  terms  the  decrease  in  density  of  the  urban  system  as  a  whole.  This  is  due  to  the  way   the   new   spaces   have   been   arranged,   which   allows   defining   the   development   as   a   form   of   urban   sprawl.  The  outstanding  increase  of  the  frequency  value  clearly  reproduces  the  strong  concentration   of  shortest  paths  towards  a  small  number  of  highly  crowded  lines,  hence  highlighting  the  presence  of   a  relevant  transport  problem  and,  what  mainly  concerns  our  issue,  a  significant  decrease  in  network   resilience.   As   a   matter   of   fact,   it   means   that   in   the   last   60   years   of   uncontrolled   urbanization   the  

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V  Cutini  &  V  Di  Pinto

 

On  the  slopes  of  Vesuvius:  Configuration  as  a  thread  between  hazard  and  opportunity

 

 

66:11   Vesuvian  system  appears  much  more  vulnerable,  in  that  it  results  more  exposed  to  the  isolation  of   some  of  its  parts  and  may  even  collapse  under  a  disaster.  

 

 

Table  3:  The  comparison  of  resilience  indexes  among  the  three  urban  scenarios  

 

With   regard   to   the   motorway,   the   comparison   between   SC_2015   and   SC_2015_MWY   expresses   a   substantial   equivalence.   The   only   parameter   that   appears   significantly   modified   is   the   frequency   coefficient,  decreasing  and  hence  showing  a  more  uniform  distribution  of  global  choice.  Such  result   can   be   interpreted   as   the   likely   effect   of   the   presence   of   the   motorway,   which   supplements   the   urban   streets   and   improperly   reinforces   their   role   of   connection   all   over   the   area,   thus   actually   enhancing   the   resilience   of   the   system.   It   has   to   be   noted   that   such   a   role   of   supplement   and   support  highly  complicates  the  ordinary  working  of  the  A3,  the  backbone  of  the  Italian  road  network   as  well  as  the  most  used  and  crowded  national  motorway,  which  is  actually  subject  to  continuous   problems   of   traffic   congestion.   Motorway   A3   here   appears   assuming   a   promiscuous   function,   as   significant   local   movement   comes   on   top   of   the   heavy   road   traffic   running   down   the   Italian   peninsula.  

The  scenario  SC_2015_MWY  was  then  analysed  by  Principal  Component  Analysis  (PCA),  as  described   elsewhere   (Esposito   and   Di   Pinto,   2015),   which   provided   a   graph   of   two   significant   principal   components.  On  such  graph  each  line  of  the  segment  map  is  represented  by  a  single  point,  whose   position  results  from  the  combination  of  10  configurational  variables,  at  a  global  and  local  scale.  The   grouping  of  those  points  allows  a  hierarchical  cluster  analysis,  which  provides  three  homogeneous   groups,   representing   aspects   of   the   working   of   the   Vesuvius   area   in   the   selected   scenario.   In   particular,   one   of   these   groups   mainly   depends   (in   statistical   terms)   on   local   configurational   variables,  thus  describing  the  structure  of  urban  phenomena  at  a  local  scale  (for  example,  movement   in   residential   areas).   With   regard   to   the   findings   of   our   case   study,   the   lines   representing   the   Motorway   A3   belong   to   the   group   of   lines   that   are   critical   for   the   local   functioning   of   the   urban   system  (fig.  8);  what  is  actually  confirmed  by  the  distribution  of  traffic  flows  between  the  motorway   nodes  within  the  whole  area.  

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V  Cutini  &  V  Di  Pinto

 

On  the  slopes  of  Vesuvius:  Configuration  as  a  thread  between  hazard  and  opportunity

 

 

66:12     Figure  8:  Principal  Component  Analysis  of  SC_2015_MWY’s  segment  map:    the  cluster  of  lines  that  play  a  crucial  

role  in  the  global  (red  lines)  and  local  behaviour  (green  lines)  of  the  system  

5.  Conclusions  

In   conclusion,   three   main   issues,   hereinafter   roughly   summarised,   seem   to   arise   from   the   results   above.   First,   the   spontaneous   and   uncontrolled   development   of   the   Vesuvian   area   has   gone   providing   slightly   positive   effects   on   the   spatial   possibility   of   coming   out   of   the   conurbation,   as   a   result   of   the   moderate   increase   of   escape   routes   from   the   area.   Moreover,   the   lowering   of   the   density   of   the   system,   due   to   the   spatial   organization   of   new   development   areas,   widespread   all   over  the  conurbation,  is  likely  to  expose  more  people  at  risk  of  being  isolated  and  cut  off  in  the  event   of  a  catastrophic  eruption.  Furthermore,  the  A3  motorway  actually  appears  to  play  a  decisive  role   supporting  the  local  transport  system  in  the  area,  whether  in  the  case  of  catastrophic  event  or  in   everyday   ordinary   behaviour;   even   tough,   as   stressed   above,   such   role   involves   serious   traffic   problems.  

We  can  conclude  from  this  that  the  development  of  the  last  decades  has  significantly  reduced  the   resilience  of  the  whole  area,  thus  increasing  its  vulnerability  to  possible  eruptions.    The  expectation   that  the  fear  of  the  volcano  could  be  somehow  interiorized  in  the  behavioural  choices  of  the  local   communities  -­‐  so  as  to  influence  and  orient  the  development  of  their  settlement  -­‐  remains  actually   disappointed:   in   such   influence   the   attractiveness   of   the   locational   qualities   of   Mount   Vesuvius   seems  to  have  played  a  far  greater  role  than  the  recollection  of  past  eruptions,  which  evidently  have   gone  fading  from  the  historic  memory;  just  as  happened  at  the  times  of  Strabo.  It  is  to  be  hoped  that   the  poor  resilience  here  verified  won’t  be  actually  put  to  the  test  in  the  foreseeable  future.  

       

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V  Cutini  &  V  Di  Pinto

 

On  the  slopes  of  Vesuvius:  Configuration  as  a  thread  between  hazard  and  opportunity

 

 

66:13  

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