ESS terms in Human populations and urban systems

The transfer of acids and acid-forming gases and particles from the atmosphere to the ground, either dissolved in precipitation (wet deposition) or as gases and particles (dry deposition).

Rain, snow or fog with a pH below that of unpolluted rain (about 5.6), caused by sulfuric and nitric acids formed from sulfur dioxide and nitrogen oxides in the atmosphere.

A pair of back-to-back horizontal bar graphs showing the number or percentage of males and females in each age group of a population, with the youngest at the base.

A population in which the proportion of older people, usually those aged 65 and over, is rising, because of falling fertility and rising life expectancy.

A single number on a fixed scale, calculated from measured concentrations of several pollutants, that communicates how polluted the air is and how much risk it poses to health.

The release of aluminium ions from soil minerals into soil water and streams when the soil becomes acidic, where they are toxic to fish, other aquatic organisms and plant roots.

A population policy intended to lower the birth rate, for example by providing contraception, setting limits on family size or giving incentives for smaller families.

An approach to designing buildings and urban spaces that increases people’s contact with nature, using living walls and roofs, plants, water features, natural light and natural materials.

A high-capacity bus system with dedicated lanes, stations where passengers pay before boarding and level boarding, giving speeds and reliability close to a tram or metro at lower cost.

A colourless, odourless, poisonous gas (CO) produced by the incomplete combustion of fuels, which reduces the ability of the blood to carry oxygen.

A device in a vehicle exhaust in which metal catalysts convert carbon monoxide, unburned hydrocarbons and nitrogen oxides into carbon dioxide, water and nitrogen.

Building in ways that keep materials in use, by designing buildings for disassembly and reuse, using recovered and recycled materials, and avoiding waste in construction and demolition.

The number of live births per 1,000 people in a population per year, calculated from the total (usually mid-year) population without allowing for its age or sex structure.

The number of deaths per 1,000 people in a population per year, calculated from the total (usually mid-year) population without allowing for its age structure.

A period of potential economic growth when falling fertility leaves a population with a large share of working-age people relative to dependants.

A model describing how the birth and death rates of a population change through five stages as a society develops, from high and fluctuating rates to low rates, with rapid growth in between.

The study of human populations: their size, structure, distribution and change through births, deaths and migration.

The number of dependants (people aged under 15 and 65 and over) for every 100 people of working age (15–64) in a population.

The movement of people from large urban areas to smaller towns and rural areas, so that the proportion of the population living in cities falls; also called counter-urbanisation.

The number of years a population would take to double in size if its current percentage growth rate stayed constant.

A holistic approach to planning that treats the urban system as an ecosystem, designing land use, buildings and infrastructure around the relationships between people, other organisms and the abiotic environment.

The number of people leaving an area to live elsewhere, per 1,000 people of the population they leave per year.

The movement of people, temporarily or permanently, within or across borders, mainly because sudden or gradual changes in the environment harm their lives or living conditions.

The services, information and means, such as contraception, that allow people to decide whether, when and how many children to have.

An approach to building design and construction that minimises harm to health and the environment over a building’s whole life through eco-friendly materials, low energy and water use and safe practices.

A building designed, built and operated to reduce its use of energy, water and materials and its harmful effects on health and the environment over its whole life.

A roof partly or completely covered with soil and vegetation, which insulates the building, slows rainwater run-off, cools the surrounding air and provides habitat.

Land in an urban area partly or completely covered by grass, trees, shrubs or other vegetation, such as parks, gardens, playing fields and river corridors.

A vertical surface of a building covered with plants rooted in soil or a growing medium fixed to the wall, which insulates and cools the building, traps dust and provides habitat.

A model that expresses human environmental impact (I) as the product of population size (P), affluence or consumption per person (A) and the impact of the technology used per unit of consumption (T).

The number of people moving into an area to live, per 1,000 people of the receiving population per year.

The number of deaths of children under one year of age per 1,000 live births in a year.

The average number of years a person can expect to live, usually measured from birth, if the death rates at each age at the time stay the same throughout their life.

An area of a city where the most polluting vehicles are banned or must pay a charge to enter, in order to improve air quality.

An urban area with a population of more than 10 million people.

The movement of people from one place to another with the intention of settling there permanently or for a long period, either within a country (internal) or across a border (international).

The combination of different land uses, such as housing, shops, offices, schools and leisure, in the same neighbourhood or building, so that daily needs can be met within a short distance.

The difference between the crude birth rate and the crude death rate of a population, excluding migration, given per 1,000 per year or as a percentage (divide by 10).

The difference between the number of immigrants and the number of emigrants for an area over a period, positive when more people arrive than leave.

A group of gases, mainly nitrogen monoxide (NO) and nitrogen dioxide (NO₂), formed when nitrogen and oxygen in air combine at the high temperatures of combustion; written NOₓ.

Tiny solid particles and liquid droplets suspended in the air, such as soot, dust, smoke and sulfate or nitrate particles, classified by diameter as PM10 and PM2.5.

Secondary pollutants (PANs) formed in photochemical smog from volatile organic compounds and nitrogen dioxide, which irritate the eyes and lungs and damage plants.

A brownish haze of secondary pollutants, mainly tropospheric ozone and peroxyacyl nitrates, formed when sunlight drives reactions between nitrogen oxides and volatile organic compounds.

Fine particulate matter with a diameter of 2.5 micrometres or less, small enough to reach the deepest parts of the lungs and enter the bloodstream.

Particulate matter with a diameter of 10 micrometres or less, which can be inhaled into the nose, throat and upper airways.

The percentage change in the size of a population over a year, combining natural increase and net migration.

The tendency of a population to keep growing for decades after fertility falls to replacement level or below, because a large share of its people are young adults of, or approaching, childbearing age.

A deliberate government measure intended to change the size, growth rate, age structure or distribution of a population, directly through births or migration or indirectly through social and economic policy.

A calculation of the future size and age structure of a population based on stated assumptions about future fertility, mortality and migration; a scenario rather than a prediction.

A pollutant that is harmful in the form in which it is emitted directly from its source, such as carbon monoxide, sulfur dioxide or soot.

A population policy intended to raise the birth rate, for example through child benefits, tax incentives, paid parental leave, childcare or restrictions on contraception and abortion.

The conditions that encourage people to leave a place (push factors, such as poverty or lack of services) and the real or perceived advantages that attract them elsewhere (pull factors, such as jobs).

An approach to building design that aims for a net positive effect on the environment, for example by generating more energy than the building uses, recharging groundwater or cleaning the air.

The total fertility rate at which each generation exactly replaces itself, ignoring migration; about 2.1 children per woman where child mortality is low, and higher where it is high.

Planning that increases the capacity of an urban system to resist, absorb and recover from shocks such as floods, heatwaves and supply failures, for example through flood-proof buildings and back-up energy.

A method of estimating the doubling time of a population by dividing 70 by its annual percentage growth rate.

An area outside towns and cities with low population density and small, dispersed settlements, where most land is used for farming, forestry or other open land.

The movement of people from the countryside to towns and cities, usually within the same country, which is the main cause of urbanisation.

A device in the chimney of a power station or factory that removes sulfur dioxide from exhaust gases, usually by passing them through a spray of lime or limestone slurry.

A pollutant that is not emitted directly but forms in the atmosphere when primary pollutants react with each other or with natural components of the air, such as tropospheric ozone.

The number of male births for every 100 female births in a population; about 103–107 occurs naturally, so higher values suggest sex-selective practices.

A gradual environmental change that develops over years or decades, such as sea-level rise, desertification or salinisation of land and water, and slowly undermines livelihoods.

The planning principle of housing people of different incomes, ages and social backgrounds together in the same neighbourhoods, for example by including affordable housing in every development.

The movement of people and activities from dense central areas of a city to lower-density residential areas at its edge.

A hazard that develops over hours or days, such as a flood, tropical cyclone or forest fire, and can displace people quickly.

A colourless, acidic gas (SO₂) released mainly when coal, oil and other fuels containing sulfur are burned, and by volcanoes; a primary pollutant and a cause of acid deposition.

A layer of the atmosphere in which temperature increases with height, so that cooler, denser air near the ground is trapped beneath warmer air and pollutants cannot disperse upwards.

The average number of children a woman would have over her lifetime if she experienced the current age-specific birth rates throughout her childbearing years.

Ozone (O₃) in the lowest layer of the atmosphere, formed as a secondary pollutant from nitrogen oxides and volatile organic compounds in sunlight; harmful to living things and materials.

The presence in city air of harmful gases and particles, such as nitrogen oxides, sulfur dioxide, carbon monoxide, particulate matter and ozone, added mainly by human activities, at levels that harm health or the environment.

A built-up area with high population density and a dense, continuous cover of buildings and infrastructure, used for living, working, trade, culture and social life; cities, towns and suburbs are urban areas.

The principle of concentrating housing, jobs and services at relatively high density within a limited urban area, so that the city uses less land and distances between places are short.

An approach to urban planning that creates, protects and connects habitats such as parks, ponds, canals, allotments and wildlife corridors, so that the city supports biodiversity and natural processes.

The community of organisms living in an urban area, including people, together with the abiotic environment of buildings, soil, water, air and climate with which they interact.

The growing of plants and raising of animals for food within or close to an urban area, for example in allotments, rooftop gardens, city farms, beehives or vertical farms.

An urban area that is significantly warmer than the surrounding countryside, especially at night, because of heat-absorbing surfaces, less vegetation and evaporation, building geometry and waste heat.

The process of deciding the best use of land, buildings and infrastructure in an urban area to meet the physical, social, economic, environmental and health needs of all its stakeholders.

The spread of low-density, often car-dependent development outward from a city into the surrounding countryside, so that the urban area uses more land per person.

An urban area viewed as an interconnected system of buildings, people, other organisms, transport, energy, water, goods and services, with inputs, outputs, storages and internal flows.

The shift of population from rural to urban areas, so that a growing proportion of people live in towns and cities, together with the conversion of land into dense built-up settlement.

Traditional building design developed by local communities over time, using local materials and techniques suited to the local climate and culture.

Carbon-based chemicals that evaporate easily at normal temperatures, such as unburned fuel, solvents and some plant emissions, which react with nitrogen oxides in sunlight to form photochemical smog.

A traditional tower on a building that catches wind and directs it down into the rooms while letting warm air escape, ventilating and cooling the building without electricity.