IB Geography G.2.3 Urban System Growth and Infrastructure Notes

Phnom Penh's Pipe Network Was the Same Length in 1993 as It Had Been in 1970

1. The Phnom Penh Water Supply Authority records a total distribution pipeline network of 288 kilometres at the end of 1970, made up entirely of cast iron pipelines.
2. By 1993 the same authority reports a potable water distribution network with a total length of 288 kilometres.
   1. Twenty-three years therefore passed with no gain in pipe length, because the Khmer Rouge evacuated the city on 17 April 1975 and the water system was left without use, repair or maintenance.
3. Even where no war intervenes, an urban population grows continuously while its networks grow in steps, because each step is a capital project with a start date and an opening date.
4. Infrastructure improvement over time is read by comparing two dated states of one network, which is why a single figure describes a state and leaves the direction of travel open.
5. A pair of dated network figures shows whether infrastructure expanded, reached more people or improved its service over time.

A Service Grows by Reaching Further and by Working Better

1. Extensive growth
   1. The system reaches ground and households it had never reached, which shows up as extra length of main, extra connections or extra route.
2. Intensive growth
   1. The system does more with the ground it already covers, which shows up as treatment added, hours of supply raised, losses cut or journey times shortened.
3. The two move independently, so a city can double its pipe length in a decade during which the quality of what the pipes carry stays where it was.

Five Services Leave Five Different Records of the Same City

1. Transport is recorded by route length, station count and passenger journeys, any of which can move while the other two stand still.
2. Sanitation is recorded by sewer connection coverage and by the share of collected wastewater that is treated, which are two separate steps.
3. Water is recorded by coverage, by hours of supply per day and by the share of water put into the network that is never billed.
4. Waste disposal is recorded by collection coverage, which says whose waste is taken away, and by disposal method, which says where it ends up.
5. Telecommunications is recorded by premises passed, which says where the cable lies, and by take-up, which says how many of those premises bought a service.

Medellín Built Upward in Metres Where a Road Network Grows in Kilometres

1. Commercial operation on Medellín's metro began on 30 November 1995 on a first section of Line A, between the Niquía and Poblado stations.
2. Line K, the Northeast Metrocable, came into operation on 7 August 2004.
3. Line H entered commercial operation on 17 December 2016 with a length of 1,402 metres, 42 cabins and three stations.
   1. A line of 1,402 metres barely registers in a route-kilometre total, so route length is the wrong measure for a line whose purpose is to climb.
4. Twenty-one years separate the first section of Line A from Line H, so the network on a map today is a sum of separate opening dates, each with its own decision behind it.

Extra Road Capacity Fills With Journeys the Old Road Was Suppressing

1. Widening a road lowers the time cost of a journey along it, so journeys that congestion had priced out become worth making.
2. The new traffic comes from drivers changing route, changing the hour they travel, changing mode, changing destination or travelling more often.
   1. Each of those five responses adds vehicles to the widened road with no growth at all in the city's population.
3. So a road scheme judged on its opening-day speeds and the same scheme judged some years later can report different results for one piece of road.

Chile Connected Its Cities to Sewers Decades Before It Treated What They Carried

1. The WHO and UNICEF Joint Monitoring Programme defines safely managed sanitation as use of improved facilities that are not shared with other households and where excreta are safely disposed of in situ or removed and treated offsite.
   1. The clause about treatment offsite is what makes this a measure of infrastructure, because it asks what happens to the water-borne disease risk once the waste leaves the plot.
2. Basic sanitation on the same ladder is use of improved facilities which are not shared with other households, so a household can sit at basic while its sewage reaches a river untreated.
3. Urban drinking water coverage in Chile stood at 53.5 percent in 1965 and at 99.9 percent in 2014, on the historical coverage series the Superintendencia de Servicios Sanitarios publishes for the years 1965 to 2014.
4. Urban sewerage coverage over the same series rose from 25.4 percent in 1965 to 96.7 percent in 2014.
5. In 1989 that series puts urban sewerage coverage at 81.5 percent and coverage of wastewater treatment over the total population at 8 percent, a treatment figure the regulator footnotes as covering the area of the former Servicio Nacional de Obras Sanitarias.
6. The regulator publishes a second treatment column measured over the sewered population, which stood at 9.8 percent in the same year.
7. Treatment coverage over the total population then reached 20.2 percent in 1999, 73.3 percent in 2005 and 96.58 percent in 2014.

Urban Sanitation Coverage Rose Slowly While Cities Filled Up

1. The Joint Monitoring Programme's 2025 report puts 3.4 billion people without safely managed sanitation in 2024, including 354 million practising open defecation.
2. The same report records that since 2015 the share of the population with sanitation services has risen quickly in rural areas while staying relatively flat in urban areas.
   1. Urban coverage of safely managed sanitation moved from 59 percent to 66 percent across those nine years while the rural share moved from 36 percent to 49 percent, so urban networks were extended at close to the speed the cities were filling.
3. The world population rose from 6.2 to 8.2 billion between 2000 and 2024 on the same report, so a steady share covers a rising headcount.

Phnom Penh Went from 26,881 Customers to 365,120 in Twenty-Five Years

1. At the end of 1993 the Phnom Penh Water Supply Authority had a total of 26,881 customers.
   1. More than 60 percent of them did not pay water bills, because many customers on the authority's records could not be reached while others had no access to water.
2. The number of customers had increased to 365,120 at the end of 2018, on the back of measures that included a campaign launched in 1994 to investigate water consumers in the city.
3. A customer list and a working connection are different things, which is why the authority had to rectify the list before the connection count meant anything.
4. Non-revenue water is the share of water put into a distribution network that is never billed to a customer, covering physical leakage, unmetered use and unauthorized connections together.
5. The authority reports the same quantity under the heading of non-revenue water, at 72 percent of total production in 1993, at 21.5 percent in 2002 and at about 8.75 percent in 2023.
6. Hours of supply per day is the measure that separates a network reaching a house from a network delivering to it, because an intermittent supply leaves the pipe empty for part of every day.

New York Closed Its Landfill in 2001 and Replaced It with a Haul Network

1. The City of New York established the Fresh Kills Landfill on Staten Island in 1948.
2. At its 1986-87 peak of operation the site received as much as 29,000 tons of trash per day and employed 680 people.
3. The landfill received its last barge of garbage on 22 March 2001.
   1. Closing a disposal site removes capacity from a system whose input carries on arriving every morning.

The Disposal Step Crossed the City Boundary While Collection Stayed Inside It

1. Since the city's 2006 solid waste management plan, four marine transfer stations accepting putrescible waste have been completed, one in Manhattan, two in Brooklyn and one in Queens.
2. At most of those transfer stations waste is containerized and moved out of the city by rail, or by barge to rail, on the New York City Department of Sanitation's own account.
3. The Port Liberty container terminal on Staten Island exports nearly 60 percent of the department-managed waste brought to those transfer stations, with the TRANSFLO terminal in Elizabeth, New Jersey, exporting the remaining 40 percent.
4. So a hole in the ground was replaced by a network of transfer stations, containers and rail, which moved the disposal step outside the boundary of the city that generates the waste.
5. The department collects 24 million pounds of trash, recycling and compostable material every day and operates 59 district garages.

Collection Coverage Is the First Thing a Waste System Has to Buy

1. World Bank figures put global waste generation at 2.56 billion tonnes in 2022, a level the 2018 edition of the same series had not expected before 2030.
2. Under a business-as-usual scenario the same source sets that figure growing to 3.86 billion tonnes by 2050, a 50 percent increase in under three decades.
3. Waste collection rates are as low as 31 percent in Sub-Saharan Africa and 67 percent in South Asia on those figures.
   1. A collection rate below half leaves most of a city's waste outside the formal system, so an incinerator buys such a city little until the waste reaches its gate.

Full Fibre Reached 78 Percent of United Kingdom Residential Premises by July 2025

1. As of July 2025, 78 percent or 23.7 million residential premises across the United Kingdom had access to a full-fibre broadband network, on Ofcom's Connected Nations report of November 2025.
2. That is an increase of nine percentage points, or 3 million premises, compared with July 2024.
3. The same report puts full fibre at 81 percent of urban premises and 61 percent of rural premises.
4. Availability here counts premises the network passes, so an address is counted whether or not anyone inside has ordered a service.
5. A fixed network costs by the kilometre of duct and can earn only from the premises it passes, so the ground carrying more premises per kilometre is built first.

Take-Up Runs Ahead in the Countryside While the Build Runs Ahead in Towns

1. Of premises with full-fibre access, 56 percent in rural areas have taken a full-fibre service, compared with 40 percent in urban areas, on the same report.
2. A city reaches high availability early, so its remaining gap sits in use once the cable has passed every door.
   1. Laying cable closes one of those two gaps and leaves the other untouched, which makes them separate problems with separate costs.

London Built Its Main Drainage in the 1860s and Was Still Adding Tunnels in 2025

1. Thames Water, Transport for London, the Office of Rail and Road and the Office for National Statistics each publish dated figures for London's sewers, railways and population, so a stage in the city's record can always be traced to a named body and a named year.
2. Any city whose authorities publish dated figures for its networks carries the same argument, so the one your own class studied is the one to use.
3. The summer of 1858 produced the Great Stink on the tidal Thames.
4. The London Museum records the main drainage that answered it as officially opened in 1865 and the whole project as completed in 1875.
5. The Institution of Civil Engineers records the whole system as 1,300 miles of sewers and 82 miles of west to east intercepting sewers, which is about 132 kilometres of interception.
6. London's mid-2023 population was 8.945 million on the Office for National Statistics mid-year estimate published in July 2024.
   1. A system the Institution of Civil Engineers records as designed in the 1860s for a city of around 4 million now underlies a city of more than twice that number, which is why heavy rain still drives it to spill.

Three Modern Stages Added Storage to a Network That Was Full

1. Five treatment works at Beckton, Crossness, Riverside, Long Reach and Mogden were upgraded in 2014.
2. Thames Water records those works as having stopped over 40 million tonnes of sewage a year from being discharged into the Thames.
3. The Lee Tunnel, built in 2016, runs 7 kilometres from Abbey Mills pumping station to Beckton sewage treatment works.
4. The same utility records it as capturing over 5 million tonnes of sewage every year that would previously have discharged into the River Lee.
5. Tideway records the 25 kilometre Thames Tideway Tunnel as connected to the Lee Tunnel in May 2024 and as fully connected and operational in February 2025.
6. The Institution of Civil Engineers puts the tunnel as connecting with 34 of the most polluting overflow points along the river.
7. Thames Water states the expected effect as reducing combined sewer overflows in a typical year by 95 percent, taking over fifty sewage spills a year down to around five.

A Railway Opened in 1863 Is Still Opening Lines and Now Carries a Radio Network

1. London Underground's history dates back to 1863, when the Metropolitan Railway opened between Paddington and Farringdon serving six intermediate stations.
2. Transport for London records the network as having grown to 272 stations and 11 lines since then.
3. Quarterly passenger journeys on the Elizabeth line, which opened in May 2022, rose from 21.8 million in April to June 2022 to 63.3 million in October to December 2024.
   1. Those quarterly figures come from the Office of Rail and Road's passenger journeys by operator series, so they count journeys, where one passenger making two trips counts twice.
4. A 20-year concession to deliver mobile connectivity across the London Underground network was awarded in June 2021.
5. By 14 January 2026, 62 of the 121 Tube stations located underground were receiving mobile coverage in their ticket halls, corridors and platforms, alongside the whole of the Elizabeth line, where the same rollout was completed in December 2024.
   1. Fitting a radio network into tunnels already dug leaves the length of the railway where it was and changes what a passenger can do inside it.

Singapore Added Water, Sewerage, Transport, Waste and Digital Capacity in Planned Stages

1. PUB's Four National Taps combine local catchment water and imported water with NEWater, introduced in 2003, and desalinated water, added in 2005.
2. Phase 1 of the Deep Tunnel Sewerage System was completed in 2008 with a 48-kilometre deep tunnel and 60 kilometres of link sewers carrying used water by gravity to Changi Water Reclamation Plant.
3. The first MRT passenger service ran in 1987, while Electronic Road Pricing was introduced in 1998 to manage demand on congested roads rather than relying on added road capacity alone.
4. Waste-to-energy incineration began in 1979 and reduces waste volume by about 90 percent, while Semakau Landfill has received incineration ash and non-incinerable waste since 1999.
5. The Smart Nation vision introduced in 2014 made digital networks a shared platform for services including transport, health, education and environmental management.
6. These projects were built in different decades but function as one urban system, because used water becomes a water source, incineration conserves landfill space and road pricing changes how transport capacity is used.

An Infrastructure Claim Needs a Service, a Measure, a Boundary and Two Dates

1. Service names which of the five systems is being discussed, because a city can improve one and leave another alone in the same decade.
2. Measure names what is counted, since length, connections, population served and volume moved answer different questions.
3. Boundary names the area the figure covers, which decides whether a movement counts as growth or as a transfer across a line.
4. Two dates turn a state into a change, because one figure on its own says only where a system stood.

Reading the Chilean and the Cambodian Series Side by Side

1. Chile's series shows a country adding the treatment step decades after the connection step, with treatment coverage over the total population moving from 8 percent in 1989 to 96.58 percent in 2014.
2. Phnom Penh's series shows a utility recovering supply from inside its own network, with water loss falling from 72 percent of total production in 1993 to about 8.75 percent in 2023.