This could be encouraged and coordinated with "bigger" farming by national policy. But better perhaps regional in the sense regions of the world. See Michel Barnier's position in favour of regional common agricultural policies.
Trade is not intrinsically a bad thing: moving flour slowly (train and sail boat will do!) from continental Europe to Ireland and shipping meat back seems sustainable if you're not assuming civilisational collapse. Flying lettuce around the planet is another issue, of course.
I guess what I'm thinking here is some form of subsidiarity for food - it should be produced as locally as makes sense. I suspect a lot of this would be sorted out simply by pricing the externalities into the shipping and production methods. Maybe a properly regulated market is the best way of doing the job?
What is efficiency?
Understanding also that regional policy, (eg CAP), can deal with the coordination of a lot of the differences between local capacities.
How far do you think that by "efficiency", you are in fact thinking of comparative advantage?
Isn't comparative advantage more-or-less about efficiency?
What kind of efficiency is comparative advantage about?
However, an urban market ... whether a market in a city or the market consisting of a small town ... is an essential element in sustainable agrarian development, so the level at which food self-sufficiency becomes a goal to consider adopting is the local region, consisting of an urban core and its rural hinterland.
Of course, legalists always want boundaries for definitions, and so units of analysis like local regions give them hissy fits, because its hierarchical ... one local region consisting of a small town and surrounding countryside is part of the hinterland consisting of a small city and its surround small towns and countryside, and that is part of the hinterland of a large city and its surrounding small cities and their surrounding small towns and countryside.
And of course in many high income nations we have planted large, difficult to heat and cool single occupancy homes directly across that countryside, so we have to learn how to plant around those kinds of obstacles.
Every large nation must aim for food self-sufficiency. All of its main regions must aim for as much food self-sufficiency as it can achieve, and some of its regions must arrive at a surplus to the extent that some of its regions fall short.
And every local region must aim to be an active center of agriculture development in its rural hinterland ... even if the peasantry in the rural hinterland presently drive SUV's to work in cubicles eighty kilometres away. I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.
a negative effect on fighting global warming and resource efficiency
Because of..?
Unless that is you simply mean local in the sense more stuff from within a few hundred kilometers and less stuff coming in from halfway across the world. If so I agree, at least in areas that have plenty of suitable land nearby. For places like the US southwest where that isn't the case you'll actually see less of that sort of 'local', though what agriculture there is in such areas will be more oriented towards the local market rather than commodity production as it is now.
In the second sense (your paragraph 2), I'd use "regional" rather than local. But yes, I am against consecrating certain regions of the world "food-producing" and shipping food across the planet. To feed the world, I think we should be producing food everywhere, and aiming at reducing transport.
You are looking at one dimension of the problem, density per square kilometer at the level of a country/district ...
... but sprawl is not simply having people live outside a densely urbanized large metropolis.
Its having them live outside of a densely urbanized large metropolis, at low densities per hectare for the median occupied hectare.
Clustered suburban villages with occupied densities of 400/km^2 spread across a former suburban hinterland surrounded by truck gardens, with the occupants of the former suburban sprawl going to the closest suburban village for their main jumping off point for the regional transport system ... whether commuting to work elsewhere, traveling for shopping, education, leisure, or collecting items they have purchased ...
... that's not suburban sprawl.
But if we are going to continue having large numbers of people living in large cities ... IOW, by "going to continue", if we are going to live in that way sustainably ... then that kind of settlement system is going to have to surround those cities, because the current system of flying fresh strawberries from Chile for a supermarket in Northeast Ohio is a system that is premised on cheap and abundant energy resources ... and its economic growth is therefore premised on an inexhaustible supply of cheap and abundant energy. I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.
