First and foremost cities create prosperity, with China in particular taking hundreds of millions out of poverty as it shifted from a rural to an urban society.
However, the second recognition is that cities magnify inequalities, both with rural regions but also within the city itself.
Resolving this seeming paradox is of fundamental importance. The fairy tale from the 1980s that the benefits of growth "trickle down" is still developers’ mantra; every "world class" development promises jobs and GDP growth, while being less explicit about the international hedge funds that will be enriched by extracting money out of the local economy.
A recent report by the intergovernmental Organisation for Economic Co-operation and Development provides insights internationally. It shows how in the richer countries the biggest inequalities are often found in the largest and most productive cities. In non-spatial terms this can be seen as a manifestation of the squeeze on middle class jobs, as labour markets become increasingly hour-glass shaped. Cities offer high paying jobs, but also are the focus for the gig economy.
Despite these general patterns there are also significant variations between different cities. For example, another OECD study found that Brasilia is seven times more segregated in terms of income than is Auckland, while even within the US, Portland, Oregon is only half as segregated as Memphis.
Another finding is that the rich are likely to be the least integrated group, in terms of where they live - they keep to themselves. The exceptions to this rule are Denmark and the Netherlands, where it is the poor who are the most segregated. These findings point the finger at housing, transport and planning policies.
There was a time, long forgotten here, when a central purpose of planning was to plan and deliver development that contributed to greater equity. For example, the basic thinking behind neighbourhood units, as the building blocks of new towns, was that everyone would have more or less the same access to essential services, public open space and employment opportunities.
The idea that we would acquiesce in a situation where neighbourhoods just a few miles apart would have differentials in life expectancy of 20-25 years would have been seen as outrageous.
It is good to see that the OECD is now advocating for "inclusive growth". While the reliance on growth can be challenged in this age of Extinction Rebellion, there are some important messages for planners and urban policy makers.
Many cities are doing practical things that seem outrageously radical in a UK context.
Santa Monica in California can scarcely be described as a little Soviet, but it is investing in creating utility companies with neighbouring cities, with the aim of making renewable energy affordable.
Seoul has a people-centred plan for green jobs for unemployed people.
As the OECD says "Short-term responses limited to reactionary planning are the symptom of current urban inequalities, and put cities at risk of leaving many residents and communities behind." We know all about that.
Cliff Hague OBE is a freelance consultant and researcher