Unit 6 · Topic 6.11 · about 30 minutes · 7 parts · 12 scored checks, 3 of them multiple choice, plus 2 from earlier lessons

AP Human Geography 6.11: Challenges of Urban Sustainability

Built by Tanner Crow from College Board's course framework · Every answer key independently checked

Unit 6: 12 to 17% of the multiple-choice section

What you'll be able to do

Describe how well different attempts to meet the challenges of urban sustainability work: what each response achieves, what evidence shows it, and where it falls short.

Key vocabulary

Term	What it means	The exam trap
Urban sustainability	A city's ability to meet its residents' needs now without using up the land, water, air and energy that later residents will need.	It joins environmental problems and land-use problems, so name the specific challenge a question describes instead of saying "sustainability" alone.
Suburban sprawl	Low-density growth that spreads outward from a city's edge, with homes set apart from jobs and shops and most trips made by car.	A growing population is not the same thing; the term is about how the growth uses land.
Sanitation	The safe collection, treatment and disposal of sewage and garbage.	It is a system of pipes, plants and trucks a city must build and run, not only how clean the streets look.
Climate change	A long-term change in temperatures and weather patterns, driven mainly by greenhouse gases released by burning fuel.	Cities both add to it and suffer from it, so say which side a question is asking about.
Air and water quality	How clean a city's air, streams, lakes and drinking water are, judged by the pollutants in them.	Pollution reaches water from paved streets and lawns as well as from pipes and factories.
Ecological footprint	The area of productive land and water needed to supply what a population consumes and to absorb its wastes.	Count the land for wastes and carbon too, not only the land for food and water.
Energy use	The fuel and electricity a city's people use for travel, heating, cooling and running buildings.	How a city is laid out shapes its energy use, not only what machines its people own.
Regional planning	Planning in which the governments of a metro area or region agree on land use, transit, water and sewers across their borders.	Check whether the governments are bound by the plan or only advised by it.
Brownfield	An abandoned or underused industrial or commercial site where real or suspected contamination makes reuse harder.	Suspected contamination counts, so a site can be a brownfield before any test confirms pollution.
Remediation and redevelopment	Remediation is cleaning up a contaminated site's soil and water; redevelopment is putting the site to a new use.	They are two steps, and a site can be cleaned up and still sit empty.
Urban growth boundary	A line around a city or metro area that separates land where development is allowed and served from land kept for farms and open space.	It controls where building goes, not how many people move to the city.
Farmland protection policy	A rule or program, such as agricultural zoning or the purchase of development rights, that keeps particular farmland from being developed.	A question can describe one of these tools, such as buying development rights, without ever saying "farmland protection".

A grid map of hypothetical Metro Area H, in which each square is 2 km on a side, or 4 square km. Dark squares were built up by 2000: 20 squares, or 80 square km, around the old center, home to 320,000 people. Light squares were built up between 2000 and 2020: 40 more squares, so the built-up area in 2020 was 60 squares, or 240 square km, home to 360,000 people. Two highways cross the map, one running east to west through the center and one running southeast from it, and 28 of the 40 new squares lie in strips along them. Every other square is farmland. People per square km of built-up land fell from 4,000 in 2000 to 1,500 in 2020. — Hypothetical Metro Area H: built-up land in 2000 and 2020.

Part 1 Think first How much land does a city need?

Commit to a guess first. Being wrong now makes the right idea stick better.

Predict first

A hypothetical city of 500,000 people covers 200 square kilometers. Now picture all the farmland, forest, water and other land it takes to grow the city's food, supply its water and energy, and soak up its waste and the carbon it gives off. How does all that land compare with the city's own 200 square kilometers?

In short. Urban sustainability is a city's ability to meet its people's needs now without using up the land, water, air and energy that later residents will need.

The challenges include suburban sprawl, sanitation, climate change, air and water quality, the large ecological footprint of cities, and energy use, and they feed one another: sprawl adds driving, driving adds exhaust and greenhouse gases.
Responses include regional planning efforts, the remediation and redevelopment of brownfields, urban growth boundaries, and farmland protection policies.
Judge a response by its goal, by the evidence before and after, and by what it pushes somewhere else, such as building that jumps past a boundary into the next town.

Part 2 Learn it Six challenges and four responses

2a. Sprawl, energy use and the ecological footprint

Urban sustainability means meeting a city's needs today without using up the land, water, air and energy its future residents will need. Three of the challenges to it come from how far a city spreads and reaches.

Suburban sprawl is low-density growth spreading outward from a city's edge: houses on large lots, set apart from shops and jobs, on roads built for cars. The picture at the top of the page shows it in hypothetical Metro Area H, where the built-up land tripled while the population grew by an eighth. Sprawl turns farmland and forest into subdivisions, and every new street needs new pipes, wires and roads.

Sprawl raises energy use. People in spread-out suburbs drive farther for every errand, and detached houses lose more heat through their walls and roofs than apartments that share them. Dense neighborhoods fill trains and buses, and walking works there.

A city's ecological footprint is the area of productive land and water needed to supply what its people consume and to absorb what they throw away. A city covers a small patch of ground, but its footprint takes in farms, reservoirs, mines and forests far beyond its limits. That reach is what makes the ecological footprint of a city so large.

Quick check · Calculate

A hypothetical city has 400,000 residents and covers 40,000 hectares. Researchers estimate that each resident needs 5 hectares of productive land and water to supply what they consume and absorb their waste. The city's ecological footprint is how many times the city's own area?

Your answer times

2b. Sanitation, air and water, and a changing climate

The other three challenges come from what a city sends into its surroundings.

Sanitation is the safe collection, treatment and disposal of sewage and garbage. When a city grows faster than its sewer lines and garbage trucks can reach, waste piles up in streets and lots, and disease spreads. Building and running these systems is one of the costliest jobs a city has.

Air and water quality fall as a city grows unless it acts. Car exhaust, factories and power plants put soot and gases into the air, and on still days they hang over the city as smog. Rain washes oil, salt and litter off pavement into streams, and sewage that leaks or overflows reaches the rivers and lakes the city drinks from.

Climate change reaches cities in two ways. Cities burn a large share of the fuel that releases greenhouse gases, in their cars, buildings and power plants. And cities feel its effects: pavement and roofs hold heat, so heat waves hit hardest downtown, and waterfront districts flood more often as seas rise and storms strengthen.

The six challenges feed one another. Sprawl adds driving, driving adds exhaust and greenhouse gases, and more pavement sends more polluted runoff into the water.

Quick check · Sort it

Each card describes a problem in a hypothetical city. Tap a card, then the challenge to urban sustainability it shows most directly.

Sanitation

Air quality

Water quality

Climate change

Energy use

2c. Steering growth: growth boundaries and farmland protection

Cities respond to these challenges in several ways. The two in this chunk decide where new building may go.

An urban growth boundary is a line drawn around a city or metro area. Inside it, new housing, stores and offices are allowed and served with water and sewer lines; outside it, land is kept for farms, forests and open space. A boundary that works pushes growth inward, onto empty lots and older sites where roads and pipes already exist, and new homes are built closer together. Less land is paved, trips are shorter and fewer new pipes are needed. It has limits. If land inside runs short, housing prices rise. And a boundary binds only the government that drew it, so builders can jump past it to the next town or county.

Farmland protection policies keep particular farms in farming. A county can zone land for agriculture only, pay farmers for their right to develop it (a purchase of development rights), accept a permanent easement that bars building on it, or tax farmland at a lower rate while it stays farmed. Fields whose development rights are bought or placed under an easement stay open for good; zoning can be changed later, and a tax break ends when the land is sold for building. But buying development rights costs a great deal, most programs are voluntary, and an unprotected farm next door can still be sold for houses.

Quick check · Fill the statement

Complete the description of two responses to suburban sprawl in a hypothetical county.

The county draws an urban growth boundary, so new subdivisions are allowed only the line. Growth that cannot spread outward goes into the older towns instead, which makes those towns . The county also pays farmers for their right to develop their fields, a policy that keeps those fields in farming even if the boundary is later moved.

2d. Working across borders and reusing land: regional planning and brownfields

A metro area is usually split among many cities, towns and counties, and each one zones its own land, the fragmentation of governments Topic 6.10 describes. One town can approve a large subdivision whose traffic, runoff and smog spill into its neighbors. Regional planning efforts bring these governments together behind one plan for land use, transit, water and sewers across the whole metro area. They work when members agree to follow the plan; a plan any town can ignore changes little.

A brownfield is an abandoned or underused industrial or commercial site, such as an old factory, rail yard or gas station, where real or suspected contamination makes reuse harder. Remediation cleans up its soil and water; redevelopment then puts the site to a new use, such as housing, offices or a park. Building on a cleaned-up brownfield uses roads and pipes already in place, removes a source of pollution and takes pressure off farmland at the edge. But cleanup is slow and costly, and builders fear being held liable for pollution they did not cause, so many sites sit idle without public money.

To judge any response, ask what goal it targets, what the evidence shows before and after, and what it pushes somewhere else.

Quick check · Multiple choice

Seven hypothetical towns share one river valley, and each town makes its own land-use rules. New subdivisions in the largest town send traffic and stormwater runoff into the six others. Which response is aimed at this problem?

Common mistakes

The mistake	Why it is wrong	Do this instead
Calling any city whose population grows a case of suburban sprawl.	Sprawl is about how growth uses land: low density, spreading outward, built for cars. A city can add many people with little sprawl if it builds up and fills in.	Compare how fast the built-up land grows with how fast the population grows, and look at the density of the new areas.
Judging a response only by what happens where it was applied.	A growth boundary binds only the government that drew it, and a cleanup on one site does not reach the next. Growth and pollution can move to a place the response does not cover.	Ask what the response pushed somewhere else: look at neighboring towns, at the land just outside a boundary, and at prices inside it.
Measuring a city's ecological footprint by the land the city covers.	The footprint counts all the productive land and water needed to supply what the city uses and absorb its wastes, and most of that land lies outside the city.	Multiply the land each person needs by the number of people, then compare that total with the city's own area.

Part 3 Watch it done Did the growth boundary save farmland?

Watch each step, then do the last one yourself.

Hypothetical Ridge County drew an urban growth boundary around its towns. Its neighbor, hypothetical Lake County, drew none. In the ten years before the boundary, Ridge County lost an average of 800 hectares of farmland a year to development, and Lake County lost 200. In the ten years after, Ridge County lost 300 hectares a year, and Lake County lost 500. Describe how effective the boundary was at protecting farmland in the two-county region.

Predict first

Before the steps, how well do you expect the boundary worked for the two counties together?

Step 1 · Name the goal and the evidence
A growth boundary aims to slow sprawl onto farmland, so the evidence to read is hectares of farmland lost each year, before and after the boundary.
Step 2 · Look where the boundary applies
In Ridge County, the loss fell from 800 to 300 hectares a year. That is a drop of 500, and 500 ÷ 800 = 62.5 percent. Judged on Ridge County alone, the boundary looks very effective.
Why this step?
Why look at Lake County at all, when the boundary is in Ridge County?
A boundary limits building only where the government that drew it has power. Builders kept out of Ridge County's farmland can buy land just across the county line, and Lake County's loss rose from 200 to 500 hectares a year. That rise has to be weighed against what Ridge County saved.
Your step · Calculate

Finish it. Add the two counties' farmland lost per year before the boundary, and again after it. By what percent did farmland loss across the two-county region fall?

Your answer percent

Part 4 Try it Choose the response

Try it · Match

A hypothetical metro area is trying four responses to its sustainability challenges. Match each response to the action that carries it out.

Try it · Decide and justify

Hypothetical City W loses about 600 hectares of farmland a year to new subdivisions at its edge. Inside the city, 90 hectares of closed factories and rail yards with contaminated soil sit empty, beside roads, sewers and a rail line already in use. The council can fund one project this year. Which does more to reduce suburban sprawl?

Which reason supports your answer?

Part 5 Explain it Explain how a metro area can grow sustainably

Nothing you type leaves this page. Check your answer against the model and each scoring point.

Free response is 50% of the exam score. This one is shaped like Question 1, from free-response II.

Free-response practice · Question 1 style

A hypothetical metro area of 2,000,000 people is spreading outward. Subdivisions of houses on large lots are replacing farms at its edge, its residents drive farther each year, and its old industrial district is full of closed factories. Each of its 15 local governments makes its own land-use rules.

(A) Define suburban sprawl.

(B) Describe one way suburban sprawl increases a metro area's energy use.

(D) Describe one challenge to urban sustainability, other than sprawl, energy use and the ecological footprint, that rapid growth creates for a metro area.

(E) Explain how the remediation and redevelopment of brownfields in the industrial district could reduce the loss of farmland at the metro area's edge.

(F) Explain one limitation of an urban growth boundary drawn by only one of the 15 local governments.

(G) Explain how a regional planning effort could make an urban growth boundary more effective in this metro area.

Your answer stays on this page. It is never sent or saved.

Model answer

(A) Suburban sprawl is low-density growth that spreads outward from a city's edge, with homes on large lots set apart from shops and jobs, so most trips are made by car.

(B) Homes in sprawling suburbs are far from work, school and stores, so residents drive longer distances for each trip and burn more fuel. Detached houses also lose more heat than apartments that share walls, so they need more energy to heat and cool.

(C) The ecological footprint counts all the productive land and water needed to supply a city's food, water, energy and materials and to absorb its waste and carbon. A city grows almost none of its own food and makes little of its own energy, so most of that land lies on farms, in reservoirs and in forests far outside the city.

(D) Sanitation: when the metro area grows faster than its sewer lines and garbage collection, waste is left untreated or uncollected in new neighborhoods, which spreads disease and pollutes streams.

(E) Cleaned-up brownfields are building sites inside the metro area that already have roads, water and sewer lines. Homes and offices built there take in growth that would otherwise spread onto farms at the edge, so less farmland is converted.

(F) A boundary binds only the government that drew it. Builders kept out of that town's farmland can build just across its border in one of the other 14, so the farmland loss moves instead of falling.

(G) A regional plan adopted by all 15 governments can draw one boundary around the whole metro area. Builders can no longer move just across a town line to escape it, so more growth goes inward, and the governments can also plan transit and sewers to serve the denser areas inside the line.

Score your own answer. This is a self-check, not a grade. Tick each point your answer makes.

(A) and (B): defines sprawl as low-density growth spreading outward, built around the car, and describes one way it raises energy use, such as longer car trips or detached houses that need more heating and cooling.
(C): explains that the footprint counts the productive land and water needed to supply what the city uses and absorb its wastes, and that most of that land lies outside the city.
(D): describes one other challenge, such as sanitation, climate change, or air or water quality, and ties it to rapid growth.
(E): explains that cleaned-up brownfields give the metro area building land inside it, with infrastructure in place, so growth goes inward instead of onto farms at the edge.
(F) and (G): explains one limit of a single government's boundary, such as builders moving across the border or higher housing prices inside it, and explains that a regional plan sets one boundary for all 15 governments, so growth cannot simply move across a town line.

Part 6 Check yourself Two metro areas, one population

The case questions use the table. The others mix the ideas from the whole lesson.

Hypothetical Metro Area N and hypothetical Metro Area S each have 1,200,000 people. A state agency published these figures for last year. Every number is invented for this lesson.

Metro Areas N and S (hypothetical), last year
Measure	Metro Area N	Metro Area S
Population	1,200,000	1,200,000
Built-up area	480 sq km	1,500 sq km
Average distance driven per resident per day	16 km	38 km
Farmland converted to development	250 hectares	1,900 hectares
Days with unhealthy air	8	27
How land-use rules are made	One regional plan with an urban growth boundary, adopted by all 12 local governments	Each of its 20 local governments makes its own rules

Case question 1 · Multiple choice

Which statement about the two metro areas does the table best support?

Case question 2 · Calculate

How many people live in each square kilometer of Metro Area S's built-up area?

Your answer people per sq km

Case question 3 · Multiple choice

Metro Area S's leaders want to cut the farmland it converts each year without pushing new building from one of its towns into another. Which response best fits that goal?

The rest stand on their own and do not use the case.

Check yourself · Spot the error

A student judges a hypothetical city's urban growth boundary. Which line is the first to go wrong?

Check yourself · Select all

A hypothetical county's farmland protection policy buys the development rights of farmers who volunteer to sell them. Which two are limitations of this policy? Select two.

Select 2 answers, then check.

Part 7 Keep it Bring back earlier ideas

This lesson stands on Topic 6.10's urban challenges and Topic 6.9's urban data.

From 6.10 Challenges of Urban Changes · Multiple choice

In a hypothetical city, a district along an old rail line has two thirds fewer residents than in 1990. Home values there have fallen by half, lenders turn down loans for the district, and its empty lots are used for illegal dumping. Which term best names this district?

From 6.9 Urban Data · Decide and justify

A hypothetical city plans a new rail station in one of its neighborhoods. Before it builds, the planning office wants to learn how long-time residents of that neighborhood feel about the station. Which data should the office gather?

Which reason supports your answer?

In three lines

Challenges: suburban sprawl, sanitation, climate change, air and water quality, a large ecological footprint and energy use, each feeding the others.
Responses: regional planning efforts, brownfield remediation and redevelopment, urban growth boundaries and farmland protection policies.
Judge a response by its goal, the evidence before and after, its costs, and what it pushes somewhere else.

Unit 6 check: 11 questions from every lesson in Unit 6

Exam strategy for this topic

Section I, Multiple Choice: 60 questions in 60 minutes.
Section II, Free Response: 3 questions in 75 minutes.

When a question asks how effective a response is, name its goal, give one thing it achieves with evidence, and give one limit, including where the problem could move, such as across a border to a town the response does not cover.

Questions students ask

What is the difference between an urban growth boundary and a farmland protection policy?

A growth boundary is one line around a city or metro area that decides where building may go. A farmland protection policy works farm by farm, through zoning, buying development rights, easements or lower taxes, to keep particular fields in farming. Many places use both.

Does a brownfield have to be polluted?

It has real or suspected contamination. Even the suspicion makes buyers, lenders and builders wary, which is why many brownfields sit empty until someone tests and cleans them.

Why does sprawl use more energy?

Homes far from jobs and stores mean longer car trips, and transit has too few riders to run often at low density. Detached houses also lose more heat than apartments that share walls.

Is climate change a cause or an effect of how cities work?

Both. Cities burn much of the fuel that releases greenhouse gases, and they face its effects, such as hotter heat waves downtown and more flooding along their waterfronts.

Are the places and numbers in this lesson real?

No. Every city, county, metro area and number here is hypothetical, chosen to show each challenge and response clearly. Real places show these patterns more loosely.

Course alignment, for teachers

AP Human Geography topic 6.11, Unit 6: Cities and Urban Land-Use Patterns and Processes.

Skill 2.D: Explain the significance of geographic similarities and differences among different locations and/or at different times.

This lesson maps all 2 essential knowledge statements of the topic to the part that teaches each one: 2 are checked by a scored question. The map is in the lesson file.