Planning and demography
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Planning and Demography

  • Demography is the scientific study of human population. Demographers are very interested in: 1) Population size, 2) Population composition, 3) Population distribution, 4) Causes of changesin these factors over time, 5) Consequences of these changes over time.

  • Demographers study in detail these changes over time, investigating issues such as changes in fertility rates, mortality rates, and migration.

  • Planners are also very interested in these very same issues, but from a perspective of: --how do population changes influence the demand for and provision of infrastructure and public services --how will population changes impact the environment --how do population changes influence changes in land use

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Population Size

  • Population size: The number of people in a given geography at a given time.

    U.S., Florida, and Leon County Population 1960-2000




  • Natural Increase: The amount of population increase attributable to a greater number of births than deaths. --In US in 1990, 17 births per 1000, 9 deaths per 1000 a natural increase of 8 per 1000 (0.8%) (290 million) --World  1.8% per year for natural increase (6.26 billion)

  • Use the “Rule of 70” to determine doubling time: Divide 70 by the growth rate. So World will double population in ~39 years (70/1.8 = ~39)

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Population Distribution

  • Population distribution: The location of population across geography/space.

  • Major shifts in population distribution occurred in the Twentieth Century in the United States:

  • --Concentration: Movement from Rural to Urban/Metro Areas

  • --Deconcentration: Movement from Central Cities to Suburbs

  • --Migration from the Rust Belt to the Sun Belt

  • Planners are particularly interested in these changes and their impacts on the built and natural environments.

  • These macro-level changes have tremendous impacts upon communities of all sizes and in all areas of the United States.

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Concentration Illustrated

Roughly 4 of every 5 Americans

lives in a metropolitan area now.

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Deconcentration Illustrated

As of 2000, 1 of every 2 Americans

lives in a suburban area.

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Population Composition

  • Population composition: The characteristics of the population.

  • Among those characteristics of interest to demographers and planners are: --Age --Sex --Race/Ethnicity

  • Again, the United States experienced many changes in these attributes throughout the Twentieth Century: --An aging population --The “rise of women” --An increasingly racially and ethnically diverse population

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Population Pyramids

  • One way of looking at changes in the composition of a population is through Population Pyramids.

  • Population pyramids show the composition of a population by age and sex (percent population in all age-sex cohorts)

  • These pyramids typically show the following:

  • --Males on left side/Females on the right side

  • --Age groups as individual cohorts going from youngest on the bottom to oldest on the top

  • These pyramids can be done for different geographies and/or different racial and ethnic groups.

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Measuring Population Change

  • Population change is simply the difference in population between two points in time.

  • Change can be expressed in Absolute or Percentage terms.

  • Absolute Change: The simple difference between population figures. Negative values indicate a loss in population.

  • Florida’s Absolute Population Change 1990-2000Pop 2000 – Pop 1990 15,982,378 – 12,937,926 = 3,044,452

  • Percent Change: The relative growth rate over a period of time calculated as a percentage using the formula: [(New-Old)/Old] *100

  • Florida’s Percent Population Change 1990-2000 (Pop2000-Pop1990)/Pop1990*100

  • (15,982,378- 12,937,926) 12,937,926

* 100 =


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Example Percent Population Change Analysis

U.S., Florida, and Leon County Population Change 1960-2000





Leon Co


  • Florida and Leon County grew at much faster rates than the United States as a whole during the period 1960-2000.

  • Leon County’s growth mirrored that of Florida’s during this period.

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Components of Population Change

  • Demographers rely upon the “Demographic Balancing Equation” to very simply and elegantly summarize population change:

  • Pop2 = Pop1 + B – D + IM – OM, where

  • Pop2 = Population at a later time period

  • Pop1 = Population at an earlier time period

  • B = Births

  • D = Deaths

  • IM = In-Migration

  • OM = Out-Migration

  • The nature of population change is simple… changes can only occur through: 1) Births, 2) Deaths, or 3) Migration

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Fertility Component

  • Fertility: The number of births that occur to an individual or in a population. 

  • Fecundity: The physiological ability of individuals or couples to have children. Maximum fecundity for a population is believed to be 15 children.

  • Another key concept is the “at-risk population”. Only a certain subset of the population is “at-risk” for fertility  Women aged 12-50

  • Factors that affect fertility include: 1) Gender (Duh!) 4) Socioeconomic status 2) Age 5) Others Religion, Culture, Education 3) Race/Ethnicity

  • Common calculations related to fertility include:1) Total Fertility Rate: Average # of children in a “synthetic” family2) General Fertility Rate: #Births per 1000 women of childbearing age3) Crude Birth Rate: # Births/Midyear Population

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Mortality Component

  • Mortality: Analyzes the number and causes of deaths in a population.

  • Life Span: The upper limit to human lives is theorized to be somewhere around 120, although there are reports of some people living as long as 135 years.

  • Factors affecting mortality include: 1) Age (J-curve) 4) Race/Ethnicity 2) Gender 5) Modernity 3) Socioeconomic status

  • Common calculations related to mortality include:1) Overall Death Rate: Deaths per 1000 population2) Crude Death Rate: # Deaths/Midyear Population3) Age-Sex-Race specific survival rates: The likelihood that an individual with certain characteristics will survive the year 4) Life Expectancy: The expected number of years an individual will live if they were to live their entire life right now. In 1900~30 (worldwide) By 2000~70 (worldwide)

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Theory of the Demographic Transition

  • When taken together, mortality and fertility can combine to form four scenarios:

  • It is theorized that as countries move from less developed to more developed, they transition from a High Birth/High Death society to one of Low Birth/Low Death. It is during this transition that (it is theorized) developing countries experience a population boom. Why?

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Migration Component

  • Migration: The movement of people into and out of a certain area.

  • Migration can occur at all geographic levels. 1) Neighborhood 2) Within a county 3) Across states: Out-migration versus In-migration 4) To a different country: Emigration (out of a country) versus Immigration (into a country)

  • Migration in the United States:Approximately 20% of Americans move per year Americans move about 11 times over their lifetimes (on average)

  • Factors affecting migration include 1) Age 2) Gender 3) Socioeconomic Status 4) Race and Ethnicity