RE: Gridcells in UrbanSim

Hi Nick,
 
This is one of the changes that we have made in UrbanSim 4. In UrbanSim
3, all models ran on the gridcell geography. In UrbanSim 4 models can
run on many different geographies: gridcells, traffic-analysis-zones,
parcels, counties, or any other geographical unit you wish to use. You
can have some models run at one level of geography, and other models run
at different geographies. The "aggregate" and "disaggregate" methods
for Opus expressions allow you to access data at different geographies
if the geographies are strictly nested.
 
The choice of geography to use depends upon the data available and the
model you are using. The main advantage of gridcells was that it is
easy to compute some spatial variables from constant-sized square
gridcells. However, chopping data into gridcells also creates lots of
problems, since the gridcell boundaries rarely correspond to the useful
boundaries in the real world. For this reason we are moving to more
natural geographies for most of our models.
 
So, one way to handle your situation is to define a geography
partitioning that provides smaller polygons where you want more
resolution.
 
Hope this helps.
 
David Socha
Center for Urban Simulation and Policy Analysis
University of Washington
www.urbansim.org <http://www.urbansim.org/>
206 616-4495

________________________________

        From: users-bounces_at_urbansim.org
[mailto:users-bounces_at_urbansim.org] On Behalf Of Nick Marinopoulos
        Sent: Monday, March 26, 2007 1:27 AM
        To: users_at_urbansim.org
        Subject: Gridcells in UrbanSim
        
        

        Hi all

        I was hoping someone could help me out with a couple of queries.

        We are in the process of applying UrbanSim to an Australian
region which consists of densely populated urban areas, as well as,
sparsely populated regions in between. I was wondering (hopefully this
is not too dumb a question) if it possible to have different sized
gridcells? Obviously that would be small in the urban areas (say 150m x
150m) and large (say 450m x 450m) in the rural areas.

        If the answer were yes, then my follow-up question (again maybe
a dumb question) would be - do gridcells have to be square?

        I would appreciate it if someone could help me out.

        Thanks

        Nick Marinopoulos

        National Institute of Economic and Industry Research (NIEIR)

        +61 3 94888444

        nickm_at_nieir.com.au <mailto:snickm_at_nieir.com.au>

         
Received on Mon Mar 26 2007 - 13:07:30 PDT