We live in the age of the city. A year or two ago we passed the point where half the world's population was now living in urban areas. This is because the rapid economic development of many large but poor countries is as much about urbanisation as industrialisation. Now experts are predicting the proportion of us living in cities will rise to 70 per cent within the next 40 years.
This isn't happening by accident. People migrate from the country to the city in the confident belief - invariably more right than wrong - this will raise their standard of living.
Putting it another way, there are huge economic advantages if most of us live in big cities, packed together like sardines. Economists call these the "economies of agglomeration".
When businesses are located close to their customers, suppliers and potential employees, they can produce their goods and services at less cost. When a number of businesses in the same industry are located in the same city there are further savings.
That's the economists' conventional explanation of why we pile into cities.
More recently, Professor Edward Glaeser, of Harvard, has argued that cities - and the face-to-face contact they make possible - are the ideal bed for germinating and propagating the ideas that drive the information economy.
So, much of the rich world's affluence is owed to our penchant for crowding together. And when politicians and economists turn their mind to cities their concern is usually to ensure the economic benefits keep rolling in.
But what about the social, psychological side? Do we pay a high social or mental price for so much unnatural crowding? As a general proposition, I'm not sure we do. Most city slickers enjoy living in cities, surrounded by so many people and so much choice.
Even so, we're engaged in a tricky balancing act, enjoying the benefits of having so many around us while retaining some personal space and privacy. In the country everyone looks after each other - or so we like to think - but in the city we tend to mind our own business.
When we get this balance wrong, city living becomes more impersonal and less satisfying than it should be. In the extreme case, there can be so much keeping-yourself-to-yourself that individuals feel lonely and isolated in the midst of the crowd.
Do economists ever worry about this sort of thing? No, not their department. Do politicians? Since they're so preoccupied with matters economic, probably not as much as they should.
These issues are explored in a new report from the Grattan Institute, Social Cities, by Jane-Frances Kelly and others. Let me summarise its findings.
It finds that social connection - our relationships with others - is critical to our wellbeing. Humans are social animals. We evolved in an environment where group membership was essential to survival, so now it's built into our brains.
We form connections at three levels: intimate personal and family relationships, links with a broader network of friends, relatives and colleagues, and collective connection - our feeling of belonging in our communities.
Social connection is important to our health as well as our happiness. Loneliness can be as bad for our health as high blood pressure, lack of exercise, obesity or smoking. Australian research shows that older people with stronger networks of friends live longer.
"The importance of social connection to health and wellbeing means that, for many people, improved relationships are a much more realistic path to a better life than increased income," the report says.
The few internationally comparable statistics relating to social connection suggest Australia is doing well. On the proportion of people who have relatives or friends they can count on in a time of need, we rank sixth out of 41 mainly developed countries. On the proportion of people who feel most other people can be trusted, we rank fifth.
Even so, our degree of social connection is declining. Our average number of friends has fallen in the past 20 years, as has the number of local people we can ask for small favours. And social connection is unevenly distributed. People on lower incomes and people with disabilities have lower trust in others.
One-person households account for a quarter of all households and are the fastest-growing type. You're not lonely just because you live alone, but the risk of it is a lot higher. Being a single parent is a risk factor, as is having limited English.
The report stresses it doesn't believe in physical determinism - that design is destiny. Even so, "the shape of our cities can make it easier, or harder, for people to interact'.
"Where we live, work and meet, and how we travel between these places, has a big impact on how much time we have to connect, and who we can meet face-to-face," it says.
Social connection is becoming more widely recognised as an important goal in the design of streets and the architecture of buildings. But when major decisions about transport infrastructure and land use are made, social connection is rarely given the same priority as the movement of people and goods for employment and commerce.
Inefficient urban transport networks see much of our day swallowed up by commuting, leaving us less time for friends and family. It's simpler for people to get together to play sport if training grounds are available nearby, and it's easier to organise a picnic if you can walk to a local park.
"If our cities are to absorb larger populations and improve quality of life for all, they will need to meet our social as well as our material needs," the report concludes.
