Frequently Asked Questions
What GIS systems are required to use What if?
What if? is a stand-alone system that works with all versions of ESRI’s ArcGIS, ArcView, and all GIS systems that can utilize shape files. All of the model’s maps can be viewed with any GIS system that works with shape files.
What operating system and hardware are required to use What if?
What if? works with any version Windows that will run ArcGIS, including Windows XP and Vista.
The system requires the manipulation of large GIS data sets and so it is recommended that it be used with the fastest available workstation. A fast hard disk is particularly recommended.
What kinds of information are produced by What if?
What if? provides four options that allow you to customize the program to the kinds of data that are available for your study area. Different kinds of information are provided by each option.
Suitability Analysis Option. The suitability analysis option can be used to produce suitability maps and reports indicating the relative suitability of different areas for accommodating future land uses.
Land Use Analysis Option. The land use analysis option also allows you to produce maps showing the projected land uses for up to five projection years and for build out. In addition, it provides reports and shape files reporting the projected land uses for sub-areas you define such as census enumeration districts, political jurisdictions, school districts, and traffic analysis zones (TAZs).
Population Analysis Option. This option provides the projected land uses produced by the Land Use Analysis Option. It also produces reports and shape files recording the following projected values in each projection year for your sub-areas:
- Total population
- Group quarters population
- Number of households
- Number of housing units
- Number of vacant housing units
- Vacancy rate
- Average household size
Population and Employment Analysis Option. This option provides all of the information for the population and land use data option. In addition, it produces reports and shape files reporting the projected employment, by place of work, for up to twenty different employment sectors for your sub-areas.
What GIS data layers are required to use What if?
The only GIS layer that is required to use What if? is the study area’s existing land use. Up to 50 land use categories can be used. Four other kinds of GIS layers can be used with the four analysis options described above.
Suitability Layers. The suitability layers are used in the Suitability option to determine the supply of land that is suitable for different uses. The suitability layers may include natural features factors such as soils, slopes, flood plains, scenic areas, and landslide prone areas and proximity to man-made features such as roads and hazardous waste sites. You may use up to a maximum of 20 Suitability layers; each layer can be organized in up to five categories (e.g., slopes can be divided into five categories, 0% to <10%, 10 % to <20%, and so on).
Allocation Control Layers. The allocation control layers are used to control the allocation of projected land use demands to the most suitable locations. The allocation layers that you use should reflect the availability of GIS data and the most important factors governing development in your jurisdiction. Typical allocation controls include: existing zoning ordinances, existing or proposed master plans, existing or proposed sewer and water service plans, and thoroughfare extension plans.
Boundary Layers. The boundary layers define the boundaries for sub-areas that can be used to report the projected land use, population and employment values in each projection period. The boundary layers can correspond to any sub-areas you wish to define including census enumeration districts, political jurisdictions, school districts, and traffic analysis zones.
Display Layers. The display layers include additional map layers that can be displayed over the What if? maps to provide more informative and attractive displays. These layers can include parcels boundaries and the location of roads, streets, and streams.
What non-GIS data are required to use What if?
The non-GIS information that is required to use What if? is dependent on the analysis option, as described above.
Suitability Analysis Option. The Suitability Analysis Option only requires GIS layers showing current land uses and the natural and man-made features that will be used in the suitability analysis.
Land Use Analysis Option. This option requires information on the current and past population, housing and employment for the study area or for a larger area such as a county in which the study area is located. Most of these data are readily available for the United States are readily available from the U.S. Bureau of the Census.
Population Analysis Option. This option requires the information for the Land Use Analysis option. In addition, it requires the following current information for the census enumeration districts within the study area:
- Total population
- Group quarters population
- Total households
- Total housing units
- Vacant units
All of this information can be obtained from What if?, Inc.
Population and Employment Analysis Option. This option requires all of the information for the previous options and information on the current employment by employment sector for enumeration districts within the study area.