Re: Model not locating development projects

Quinn

First, I am assuming you are using fairly recent code and that the
development_constraints table contains max_residential_units and similar
fields rather than the earlier format that did not contain min and max
fields, and instead had a development_type field. If this is not the
case, please indicate what version of the model system you are using.

I think the problem is due to a change in the behavior of the model when
the development constraints are not specified in the table. In the
transition style developer model (the earlier model that would have used
the development constraints table that included a development_type field
in it), leaving out constraints information behaved as you expected: no
constraints meant that a cell could transition to any of the development
types. There were other issues with this transition model, but that is
not the issue so let's put that aside. The newer developer model that
uses a location choice framework handles development constraints
somewhat differently. Most importantly in your case, it uses a capacity
calculation to figure out if a project of a given size can fit into a
cell, given its available developable capacity --- which is determined
by looking up the constraints that apply to the cell and computing
whether the remaining capacity is greater than the size of the project
to be placed. That works as you expect in most cases, but not if you do
not specify any constraint information at all. In that case, it is
treated as having no capacity rather than infinite capacity. I hope that
helps explain why it is behaving as it is. Now on to what to do about it.

If you really want to see what would happen if you had no planning
constraints at all, you could put in a single development constraint
record with a -1 for the plan_type_id and a fairly high value for the
max_residential_units, max_commercial_sqft, max_industrial_sqft. I don't
think this would be very effective for estimating the model parameters,
since this is not how the world generally works. You will get better
results by estimating the model using even a rough approximation of what
the constraints actually are in local land use policy, and putting this
into the development_constraints table.

Hope this helps.

Paul

Quinn Korbulic wrote:
>
> Hello,
>
> After a twenty year model run I find that only 17 residential units
> were built, about 50,000 sqft of commercial were built and zero
> industrial. The model is developing projects but not locating them.
> One example of this is that during the final year of the run there are
> 20,000+ ‘movers’ (out of around 40,000 households) for the HLCM and
> nowhere to put them because in 20 years there has only been 17 units
> built.
>
> I have a hunch as to why this is happening: my development constraints
> table is mostly blank. With a blank development constraints table I
> assumed that development could happen and would be placed in any
> gridcell where there is no constraint defined.
>
> I would appreciate any suggestions or shared experience with similar
> problems…
>
> Thanks,
>
> Quinn Korbulic
>
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Received on Wed Jul 04 2007 - 20:14:50 PDT