Plan the city before it grows
Before the city reaches its fringe, reserve the land it will need for 20–30 years, secure an arterial grid about 1 km apart with its rights-of-way, lay a street hierarchy and utility corridors inside it, and publish the plan.
Everything for this step
- Field guide
- Planning a settlement → 12 sections Earth sciences → 7 sections
- Builds
- None yet.
- Reference sheets
- None.
- Sciences it rests on
- Engineering · Earth sciences
- Track
- Settlement and planning, level 6 of 7 · next: The compact, connected, resilient city
Why this matters
Cities grow faster in area than in people: between 1990 and 2000 urban land cover grew at twice the rate of urban population, and at those rates the world's urban population would double in 43 years while its land cover doubled in 19 (Angel, Making Room for a Planet of Cities, Lincoln Institute, 2011). Growth that arrives before the streets cannot be serviced cheaply afterwards: in Bogotá, correcting an irregular settlement cost 2.7 times as much as planning the area in the first place, and upgrading ran to about US$50–70 per m² against under US$25 to service new land (Smolka, 2003).
The cheapest lasting step is to fix the arterial roads before anyone builds: long, continuous roads spaced no more than about 1 km apart, so public transport is within a 10-minute walk of every home, with rights-of-way wide enough for bus lanes, cycle paths and trunk water and sewer mains.
The shape of it
- Project the land the city will need for 20–30 years, and plan at least 50 % more than population and density alone suggest.
- Peg an arterial grid no more than 1 km apart over the whole expansion area, connected to the existing roads.
- Secure the rights-of-way first: arterials 45–60 m, sub-arterials 30–45 m, collectors 15–30 m, local streets 10–15 m in new areas.
- Lay utilities in common ducts under the street, so pipes and cables can be repaired without digging up the road.
- Reserve parks, school and clinic sites, and flood land before the plots are sold.
- Let landowners give part of their land for streets in return for the right to develop the rest.
- Publish the plan with its map, rules and review date, and decide every permit against it.
Doing it, step by step
The summary above says what has to happen. This says how, with the numbers that decide whether it works.
1 · Project the land the city will need
Plan for 20–30 years of expansion, and plan generously. Angel's global sample of cities (Lincoln Institute, 2011) found that:
- Built-up densities fell about 2 % a year between 1990 and 2000, and have fallen for a century or more.
- Urban land cover grew twice as fast as urban population.
- Most cities in the study expanded their built-up area more than 16-fold in the twentieth century.
Project population and density together, then allow for the open land that a growing city leaves inside its footprint: the areas planned for 20–30 years of expansion should be at least 50 % larger than population and density alone suggest. Draw generous metropolitan limits, not a tight growth boundary.
2 · Peg an arterial grid about 1 km apart
The arterial grid is the frame the rest of the city fills in. Angel gives it five properties:
- Total coverage of the whole area designated for 20–30 years of expansion.
- Connectivity: long, continuous roads that cross the area and join the existing network.
- Spacing of no more than about 1 km, so public transport is within a 10-minute walk of every point.
- A wide right-of-way, of the order of 20–30 m or more, for bus lanes, cycle paths, a median and trunk water and sewer mains.
- Progressive improvement: acquire only the rights-of-way at first, and build the road in stages as the city reaches it.
Inside each roughly 1 km superblock, local streets can be laid out later, by public or private developers, to reach every plot.
3 · Give every street in the hierarchy its right-of-way
Fix the width between property lines before anyone builds; carriageways can be paved later. India's urban roads manual (IRC:SP:118-2018) gives, for new areas:
- Arterial roads: right-of-way 45–60 m, on a network of about 1,000 × 1,000 m, with room for a future mass-transit line.
- Sub-arterial roads: 30–45 m, on about 500 × 500 m.
- Collector streets: 15–30 m, on about 250 × 250 m.
- Local streets: 10–15 m, at spacings under about 125 m.
Peg each right-of-way on the ground, record it in the land register, and refuse any building that encroaches on it. The planning guide covers the earlier, smaller layouts.
4 · Put the utilities in corridors under the street
Water, sewers, drains, power and telecoms all follow the streets. Map them, and wherever feasible lay them in common utility ducts: one for city-level utilities (sewers, water, electricity) and another for street-level ones (local storm drains, telecom, street-lighting cables), so each can be repaired without digging up the road or disturbing the others (IRC:SP:118-2018).
Trunk water and sewer mains run under the arterials, sized for the whole expansion area; separate storm drainage and foul sewers as city water and sewerage requires.
5 · Reserve the public land before the plots are sold
Once land is built on, it cannot be bought back cheaply. Before plots go on sale, mark and reserve:
- Parks and playgrounds within walking distance of homes, in a hierarchy from small neighbourhood spaces to large city parks.
- Sites for schools, clinics, markets and fire stations.
- Flood land and steep slopes, kept open by zoning.
The historic plans that have lasted — Barcelona's and Manhattan's grids among them — combined a rational layout, a clear line between public and private space, and well-dimensioned streets and blocks (UN-Habitat, Planned City Extensions, 2015).
6 · Assemble the land fairly
The city does not have to buy all the land for its streets. In many countries, from Israel to Ecuador, landowners on the urban fringe may develop their land on condition that they give up part of it for public use, enforced by regulation (Angel, 2011). The arterial grid then raises the value of the land that remains.
Pay for land that must be bought — for arterials crossing a single small holding, for instance — at a published valuation, and record every dedication and purchase in the land register.
7 · Publish the plan and keep it
A plan nobody can see is not a plan. Display the map, the street classes, the reserved land and the rules in a public place and on the record, with the date it was adopted and the date it will be reviewed.
- Decide every building permit against it, and publish the decisions.
- Review the projections against the census and the built-up area at the review date, and extend the grid ahead of the growth.
- Change the plan only by a published amendment, as zoning requires.