Most planning agencies, particularly those large enough to have a research staff, do considerable research. One common type of study is the "population forecast." One cannot plan without having an idea of for how many people one is planning. It is also important to know something about the likely age structure of the population. One hundred people over the age of
65 make very different demands on the community than do 100 elementary school students.
There are various approaches to forecasting population. A common technique is the "cohort survival" method. In this, the present population is mathematically "aged" into the future.4 In other words, each age and sex group, or "cohort," of the population is advanced through time and its numbers adjusted for expected mortality. Adjustments are made for net migration (moves in minus moves out) and births. The advantage of this technique is that it presents a detailed picture of the structure of the population rather than just an estimate of the total number of people. The mathematics is relatively simple, but getting good results is another matter. At the city, county, or town level, the big differences in growth rates between places are largely due to differences in net migration. Predicting net migration accurately is difficult. At the present it is much more an art than a science.
Then, too, the interaction between plans and forecasts can muddy the waters.5 For example, in many suburban areas, housing stock is the factor that limits population growth. One might estimate net migration on the basis of past performance, but how does one factor into these estimates the effect on population of land-use control ordinances that will be enacted next year and that may be affected by this year's forecasts? In the ideal planning situation, the making of plans and the making of forecasts should be related. Such coordination is not easy to achieve.
Another basic study is the "land-use inventory."6 Such a study begins with a mapping of existing land uses (residential, industrial, commercial, educational, recreational, etc.). It also characterizes undeveloped land in terms of suitability for different uses. The common practice is to prepare a series of maps that show land characteristics such as topography, flood plains, areas of well or poorly drained soil, and so on. In many cases the land-use study also contains information on land ownership, generally distinguishing among public, private, and institutional holdings at a minimum. The study may also identify major private or major institutional holders. The study may also identify some infrastructure characteristics, particularly water and sewer services. It may also identify some legal characteristics such as zoning categories, though these are less permanent than most of the other items mentioned.
In recent years the traditional paper map for the recording of the results of land-use studies has been supplemented by electronic mapping systems generally referred to as Geographic Information Systems (GISs). In a GIS, data are stored in digital form. For example, to store a contour line in the system, a technician moves a digitizer along the contour line of a topographic map, and the path of the digitizer is converted to digital form and stored in the computer's memory. Information such as assessed values, zoning categories, census data, and the like can also be entered as numbers or letters. The electronic database can then be quickly used to produce a variety of maps, calculations, tabulations, and so on. The map that might take a draftsperson days to draw can often be produced by a GIS in a few minutes.
At the regional scale, GISs now make use of data from satellite cameras. Images, from both within and outside the visible light spectrum, come from the satellite camera in digital form and are then "imported" into the GIS database. Among the material that can be mapped from such digital information are vegetation, topography, hydrology, land use, temperature, and some geologic features. The level of precision is not usually sufficient for small parcels, but it may be quite adequate for work at a large scale and costs only a fraction of what it would cost if obtained by conventional methods.
Almost all comprehensive plans contain a circulation element. Thus studies of traffic flow characteristics along the existing transportation network are likely to be done early in the master-planning process. Some general estimates of future traffic flows based on projections of future population and employment are also likely to be made at an early stage. There is a strong interaction between transportation planning and land-use planning. The amount of development in an area is a major determinant of the number of trips that will be made to and from the area. On the other hand, the accessibility of the area will in large measure determine how much development takes place there. Thus land-use and transportation planning should go hand in hand.
Studies related to infrastructure are common. Water supply and the provision of sewer service are key elements in shaping the pattern of development in growing areas. Studies may be done to determine potential areas for sewers and areas that are amenable to the development of public water supply systems. In areas where public water and sewer supply are not feasible, studies may be devoted to groundwater supply and quality.
Soil characteristics may come in for serious study at this point. If an area is not to have sewers, for whatever reason, the amount of development that can occur may be limited by the capacity of the soil to absorb safely household wastes from septic tanks. This capacity will vary greatly with soil types. A sandy, well-drained soil may safely permit building several houses per acre. On the other hand, soil with a great deal of clay or bedrock lying close to the surface may require an acre or two of land per house for safe disposal of household waste. Soil characteristics such as shrinkage and swelling as the water content of the soil changes will affect the types of buildings that can be constructed. The capacity of the soil to absorb water will affect flooding potential, an important characteristic in considering the type and intensity of development appropriate for the area.
Many communities will do recreation studies as part of a master plan, looking at population, recreational preferences, existing facilities, and so forth. In general, such studies will inventory the present supply of facilities and services. Future needs may be estimated by applying standards (for example, so many acres of parkland per 1,000 of population) to the municipality's projected population, and by surveys that determine citizen preferences. The gap between the existing situation and the estimated need is used to establish preliminary planning goals.
Economic studies can be an important part of the research phase. Studies may be done to estimate future revenues and expenses, to estimate future land and infrastructure needs that result from population and employment change, as a guide for economic development policy, to make decisions about whether to encourage or discourage particular developments, about tax policy, and many other matters. One might suspect that because a local economy is smaller and simpler than the national economy, making reasonably good forecasts for the local economy would be less difficult. But the truth is exactly the opposite. Any local economic forecast depends in part on what happens in the national economy—employment, interest rates, inflation, and the like. Then, uncertainty about local factors is added on top of the national uncertainty. During the period 2010 to 2014 there were five bankruptcies of general purpose governments of which the largest and most publicized was that of Detroit.7 The financial crisis of 2008 and the subsequent recession was a factor in all of them, since it pushed down sales and property tax revenues, resulted in cutbacks in federal and state aid, and pushed down the value of municipal pension fund reserves, thus necessitating additional contributions by the municipalities. But only a very small fraction of economists, bankers, and financiers saw it coming. No matter how good the analyst's insight into the local economy, if he or she did not see what was coming nationally the municipality would still have been blindsided.
Forecasts of local economic trends, even apart from national questions, have many uncertainties. There is the fact of interplace competition, both from inside and outside the United States. Predicting how that will affect the local economic base is not easy. The smaller the place, the more "lumpy" economic data will be; that is to say that single decisions by firms to invest or disinvest, to move in or to move out, will produce large percentage effects on the economy. In short, forecasting the path of the municipal economy is an uncertain matter. Nonetheless, it is often an unavoidable task. It is hard to plan without having some idea of what one has to plan for and what resources will be available to finance what will need to be done. The municipality's planning and fiscal staffs may do the forecasting and financial projects, or that task may be contracted out to a consultant. A number of consulting firms now specialize in economic and financial forecasting for municipal governments.