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INTERACTIVE GROWTH MODEL (IGM™)

The IGM™ has the potential for multiple applications from developing and updating comprehensive plans to providing accurate forecasting data to develop master plans for utilities, economic development, schools, parks and updating traffic models to name a few.  The connection between the population forecast model and the IGM™ provides our clients with opportunities to customize applications for specific study areas.

The Connection between the Population Forecast to Build-out Methodology, the Interactive Growth Model™, and Sub-models

The Population Forecast to Build-out Methodology is the beginning step in the development of an Interactive Growth Model for a client. The resultant product is a forecast of the aggregate population, in five-year increments to build-out and serves as a key input to an Interactive Growth Model and thereafter to any requested sub-models.

For example, Lehigh Acres, Florida, is a fast growing community that is 96 square miles in area and has an estimated build-out population of over 300,000. The Board of County Commissioners of Lee County, Florida, the county in which Lehigh Acres is located, retained Van Buskirk, Ryffel and Associates, Inc. (VBR), to do a population forecast study and estimate the land uses required to support that population at build-out. Similarly, in another study, VBR was hired to perform detailed queries of parcels and zoning to determine the likely build-out population and the apportionment of land uses needed to support that population.

One of the end products of the Interactive Growth Model™ created for a client is the distribution of the aggregate population in five-year increments to build-out. The population distribution is by sub areas of the "community" such as Census Block Groups, Traffic Analysis Zones (TAZ's) or planning areas unique to the community. Moreover, the variables that are built into the growth model are those that are important to the jurisdiction involved.  The IGM can be used to develop What if? growth management scenarios to demonstrate the effect of alternative land use decisions made by the client and as input to short and long term budgetary considerations.

The City of Cape Coral, Florida is 114 square miles in area and was forecasted to have a build-out population of over 400,000. It was necessary to accurately forecast the aggregate population at build-out and to then apply the IGM™ to forecast its distribution over time. That city saw further applications of the IGM such as amending the future land use element of their comprehensive plan, updating their traffic models and promoting economic development.

This map is of the City of Cape Coral, Florida, a 114 square mile pre-platted community. It is a visual
depiction of how population was forecasted to be distributed over time to build-out. This visual tool
translates an enormous amount of tabular data to convey spatial concepts and outputs to public
bodies and the general population.

Collier County, Florida, is the largest county in the state in land area. VBR was retained to apply its IGM for a major portion of that county with a land area of approximately the size of the State of Delaware. In addition to creating a growth model for this study area, several sub-models will also be prepared including most of those described below.

The City of Auburn, Alabama is experiencing rapid growth and many applications for annexations. They retained VBR to apply the IGM™ to address these issues and to update their comprehensive plan.

There are several Sub-models that can be incorporated into the Interactive Growth Model during its development (most cost-effective) or at a later time, depending on the priorities of the client. Some of the sub-models and their function are as follows:

Commercial Land Use Allocation Sub-model

This sub-model determines the ideal location, timing, acreage, and building square footage needed for office and retail uses consistent with the forecasted population at build-out, disposable income of the community or for specific milestone time periods. Moreover, it is designed to locate the “commercial nodes” by type, such as neighborhood, community or regional shopping facilities, in such a manner as to reduce trip lengths for the population served. In this sub-model, as it is true in ALL of our sub-models, they can be used to update the future land use designations within the client’s Comprehensive Plan

This shows the general location and timing of neighborhood, community and regional shopping
facilities that are consistent with population growth, over time, and based on the most efficient
and convenient trip lengths.

Industrial Land Use Allocation Sub-model

Industrial land use designations do not rely on population forecasts but rather reflect the community’s policy to increase and diversify its employment and/or tax base. This sub-model is used as a guideline to locate the optimum sites and building square footages consistent with the community’s standards to achieve the desired ends.

School Plant Allocation Sub-model

This sub-model is used to determine the optimum location, timing, size and type of school plant facilities that will be needed to serve the forecasted school age population over time. State and local guidelines are used to develop this sub-model depending on local and state law and requirements. 

Parks, Recreation and Open Space Sub-model

This sub-model will forecast the demand for park and recreational space by various park classifications (neighborhood, community and regional parks), the timing of facilities and their optimal locations in 5-year increments to build-out.   It can be used to determine the best spatial distribution of parks based on service area, time, population and demographics.  This sub-model can be updated every five years for scheduled capital improvement programs and provide input for a master recreation plan or to test or revise existing master plans.

Fire Station Sub-model

The fire station sub-model determines the optimal timing and location of fire stations consistent with the projected population, its location over time and desired response time. The criteria for the location of fire stations will be those established by the Insurance Service Office for service area and response times.

Firehouse locations and timing are shown above that are consistent with population growth and
distribution over time, and based on prescribed response times to that population.

Affordable Housing Sub-model

This sub-model is used to develop, based on a pro-rata formula, the percentage of affordable housing units vs. total dwelling units needed to build-out, by five-year increments and serve as a guide to determine optimal locations.

The IGM™ can be applied to various study areas such as cities, towns, counties, metro areas and regions to generate accurate forecasting data for multiple applications. For, example, the IGM™ and its sub-models, can be used as the core for a comprehensive plan or to update an existing one.

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