Building  a  Network  Data  set  from  scratch    Building  a  Network  Data  set  from  scratch  is  challenging.    This  challenge  is  usually  due  to  varied  quality  of  the  street  data  that  comes  as  a  mapped  layer  from  government  agencies.    It  often  takes  several  iterations  (often  including  building  topology  to  make  sure  all  the  lines  [streets]  are  connected)  before  one  can  achieve  a  good  network  for  modeling.    This  is  likely  the  reason  why  many  in  industry  purchase  prebuilt  networks    from  companies  like  Navteq.    However,  it  is  possible  to  do  this  yourself  but  one  never  knows  how  clean  the  data  is  that  you  download  from  a  government  server.    Here  is  a  link  to  several  streets  files  and  a  few  prebuilt  networks  in  California:    http://ratt.ced.berkeley.edu/downloads/BayAreaStreets/Bay_Area_Streets.html    I  have  included  the  steps  to  download  and  build  a  network  dataset  for  the  county  of  San_Joaquin,  CA.    You  can  input  your  data  where  I  use  Stockton  in  the  text  below  and  build  your  own.    My  notes  are  extremely  cryptic  here  as  they  are  meant  to  complement  the  lab  10  assignment.    I  saved  the  Transportation  network  in  a  geodatabase  called  SN1Geodatabase.gdb.    I  include  in  the  picture  the  two  original  shape  files,  one  was  a  county  polygon  and  the  other  was  the  transportation  network  of  San_Joaquin_Streets.    After  I  build  the  network,  I  load  it  to  ArcGIS,  displayed  here  in  the  following  set  of  graphics.  

 

 

 

 

 

 

 

 

 

 

 

 

 

Building  your  own  Network    for  Network  Analyst  

Start  ArcCatalog  

Click  Customize !  Extensions    

Check  Network Analyst  

Next  ….  Create  a  File  Geodatabase  

 

I  call  this  one:    SN1Geodatabase.gdb  

 

I  then  Create  a    New  Feature  Dataset  

 

I  Call  it  Transportation  

 

 

I  set  its  Projections  and  Datum.    I  make  it  the  same  as  the  original  San_Joaquin_Streets.shp  shapefile.      

 

I  import  the  shapefile    (San_Joaquin_Streets.shp)  into  the  Geodatabase  as  a    Feature  Class    

 

 

 

and  call  it  Streets   .  

I  then  drag    it  into  the  Transportation  Feature  Dataset  

 

 

I  then  add  fields  to  the  Streets    Feature  Class  

The  Fields  and  Process  of  Adding  fields  to  data  base:  

 

 

 

Call  it  METERS  and  make  it  Floating  Point.  

 

Calculate  METERS  of  each  line  segment  

 

 

 

 

Add  a  field  MeterPm    to  calculate  SPEED  in  Meters/Minute  .    We  want  to  model  in  increments  of  minutes  of  time  traveled.  CONVERSION  from  miles/hour  to  Meter/minute  is  needed  for  this  as  we  are  in  a  projection  that  deals  in  METERS  and  in  a  city  we  likely  want  to  model  in  Minutes  rather  than  Hours.  

 

 

Calculate  

MeterPm = SPEED * 26.82

 

 

Result  looks  like  this  

 

Add  2  fields  to  calculate  how  long  it  takes  to  travel  the  length  of  each  line  segment.    These  fields  are  the  time  to  go  From  node  -­  To  node  direction,    (FT_Minutes)

 

and  the  time  to  go  To  node  -­  From  node  direction  (TF_Minutes)  

 

 

 

 

 

 

 

 

 

 

 

 

Result  looks  like  this  

 

Calculate  FT_Minutes = [METERS] / [MeterPm]  

 

 

and  then  TF_Minutes = FT_Minutes  

 

We  do  this  incase  later  the  time  will  increase  moving  in  one  of  the  directions.      

 

 

 

Result  looks  like  this  

 

 

 

With  the  fields  created  we  can  now    create  a  new  Network  dataset  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

These Network attributes are properties of the network that control navigation. Common examples are cost attributes that function as impedances over the network and restriction attributes that prohibit traversal in both directions or one direction, like one-way streets. Network Analyst analyzes the source feature class (or classes) and looks for common fields like Meters, Minutes (FT_Minutes and TF_Minutes, one for each direction), and Oneway. If it finds these fields, it automatically creates the corresponding network attributes and assigns the respective fields to them. (This can be viewed by clicking the

Evaluators tab.) Click the Meters row to select it, then click Evaluators to examine how the values of network attributes are determined.

The Evaluators dialog box opens.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The  table  on  the  Source  Values  tab  lists  the  source  feature  classes.  Linear  source  feature  classes,  that  become  edge  elements  in  the  network  dataset,  are  listed  twice;  once  for  the  from–to  direction  and  once  for  the  to–from  direction.  (The  directions  are  in  relation  to  the  digitized  direction  of  the  source  line  feature  –  just  a  point  of  information  and  not  critical  to  remember  but  an  important  part  of  topology  building.)    

The  Type  column  shows  the  type  of  evaluator  used  to  calculate  the  network  attribute  values.    

The  Value  column  holds  information  the  evaluator  needs  to  calculate  attribute  values.  

 

From  the  Attribute  drop-­‐down  list,  click  each  type  of  attribute,  one  at  a  time,  and  inspect  the  evaluator  types  and  values  for  the  source  feature  classes.  

Here  I  click  Minutes:  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

After  clicking  OK  then  select  Next  >  to  move  on    

 

select  yes  here….and  finally  Next  >  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Finally  select  Finish  to  build  the  Network  dataset….  

A  progress  bar  opens  showing  you  that  Network  Analyst  is  creating  the  network  dataset.  

 

Select  Yes  

 

 

The new network dataset, Streets_ND, is added to ArcCatalog along with the system junctions feature class, Streets_ND_Junctions.

Preview the network dataset by clicking its name and

clicking the Preview tab.

Close  ArcCatalog.  

 

 

 

 

 

 

 

 

 

 

 

 

Open  ArcMap  and  add  the  New  Feature  Dataset  …  Transportation  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Make    sure  you  turn  on  the  Network  Analyst  extension  

 

 

 

 

 

 

You  are  ready  to  Network  model…..