空间规划
Jan 28th 2013, 18:12 by L.S. | LONDON
GROWTH, unemployment, industrial production—data for comparing countries is in rich supply. But if economists want to analyse and contrast cities, they have less to go on: most information is not standardised and is thus hard to compare. This is a problem, given the world’s rapid urbanisation and cities’ ever growing economic weight: the UN expects the urban population to double between 2010 and 2050, from 2.6 billion to 5.2 billion.
增长率，失业率，工业产值 — 国与国之间的对比数据可谓五花八门。但是当经济学家们想要分析或对比各个城市时，却发现做不到：大部分数据都是非标准化的，所以很难进行横向对比。鉴于全球迅猛的城市化进程以及各个城市不断增长的经济比重，这的确是个问题：联合国预计2010年到2050年城市人口数量将翻一番：从26亿增长到52亿。
A new book goes some way toward remedying this deficit: “Planet of Cities”, by Shlomo Angel*, a professor of urban planning at New York University. To make “a modest contribution toward a science of the city”, Mr Angel and his colleagues generated a lot of comparable data on things such as urban expansion, population density and open space.
纽约大学城市规划学教授什洛莫·安吉尔的新书：“城市星球”，似乎填补了这一信息空白。为了对“最城市科学略尽绵薄之力”，安吉尔先生和他的同事们给出了许多具有对比性的城市数据，例如城市扩张，人口密度和（城市里的）露天场所。
Mr Angel and his team pulled this off by developing clever methods to analyse detailed satellite images. In other words, the researchers had computers count pixels to calculate such things as the fragmentation of big cities (meaning those with a population of more than 100,000, of which there were about 4,000 worldwide in 2010, see map). To see how these cities have changed over time, the researchers picked 120 of them and looked at two sets of satellite images, one from 1990 and the other from 2000. And for a representative subset of 30 cities they made comparisons going back to 1800 by digitising and resizing old maps.
安吉尔先生和他的团队用很巧妙的方法对高精度卫星图片进行分析。具体来说，研究人员用电脑分析图片上的像素，计算出大城市是如何扩张的（指2010年全球有大约4000个人口超过10万的城市，见图）。为了弄清这些城市是如何随着时间推移而变化的，研究人员从中挑出120个城市，用两组卫星图片进行对比，一组拍摄于1990年，一组拍摄于2000年。为了对比其中代表性的30个城市，他们还特意找来老地图将其数字化然后放大，与1800年时的情形进行比较。
Some of the results are predictable. Both urban population and urban land cover have grown between 1990 and 2000 (by 1.6% and 3.66% respectively in the global sample of 120 cities). Most big cities are now “polycentric”, meaning they no longer have a single central business district. And despite the rapid growth of cities in the 20th century (sixfold in the representative sample of 30 cities), the world’s total urban land cover is still small: less than half of one percent of all land area in 2010.
一些结果不出所料。城市人口和城市面积从1990到2000年有所增加（采样的120个城市人口和面积增长率分别为1.6%和3.66%）。大城市大部分都已经“多中心化”，就是说它们不再只有一个中央商务区。尽管20世纪以来城市发展迅速（30个代表性样本城市扩张了6倍），但是全球整体城市面积还是很小：2010年城市面积只占全球陆地面积的0.5%。
But other results are surprising, in particular those which suggest the existence of “urban laws” that appear to apply worldwide. On average, cities of all population sizes are growing at the same rate. Population densities have been in decline for more than a century—and not just in rich countries, where many cities have sprawled. It also seems to be a global norm that half of a city’s footprint is not built up. And the distribution of cities within a given country indeed follows the “law” that George Zipf, an American researcher, discovered in the 1940s: that the largest city is always about twice as big as the second largest, three times as big as the third largest, and so on.
另外有些结果则出人意料，尤其是那些看似全球通用的“城市规律”。各个城市不论人口多少，发展速度基本都相同。人口密度已经持续下降超过一个世纪 — 而且不只是在城市分散化的发达国家。还有一个全球性现象，那就是城市里有一半的空间没有被利用起来。某些地区的城市分布的确符合乔治·齐普夫（George Zipf，美国研究人员）1940年提出的“城市规律”：最大的城市永远是第二大城市的两倍大小，是第三大城市的三倍，以此类推。
Using such results (and the UN’s population forecasts) Mr Angel is able to predict by how much the world’s urban land cover will grow in the decades to come. Assuming conservatively that the urban population densities decline by 1% per year (the real number since 1900 was around 1.5%), the land covered by cities will treble to 1.34% of the global land area by 2050. Yet this low average is somewhat deceptive: 29 countries will see more than 10% of their land covered by cities, including Britain, Italy and Lebanon. And in developing countries, where most urbanisation will take place and population densities are likely to decline most quickly, urban land cover may grow more than six-fold.
以此结果（还有联合国人口预报）进行计算，安吉尔先生可以预测出几十年后城市面积会增加多少。假设城市人口密度以每年1%的速度持续下降（自1990年以来实际数字是1.5%），到2050年城市面积会增长3倍，达到全球陆地面积的1.34%。这么低的比例其实有点欺骗性：因为29个国家的城市面积将会超过他们国土面积的10%，其中包括英国、意大利和黎巴嫩。大部分城市化进程和人口密度下降将发生在发展中国家里，城市面积可能会增长超过6倍。
The book, however, is much more than an interesting exercise in urban statistics. Mr Angel does not hide his agenda: he wants to demonstrate that the movement of people into cities cannot be stopped; trying to slow down urbanisation and even stop it will produce all kinds of unpleasant side effects, he argues, not least driving up housing prices—which hurts the poor the most. Seoul, which established a protected greenbelt in 1971, is a case in point. By 1990, the average household in South Korea’s capital had to pay ten times its entire income to purchase a basic housing unit.
这本书绝不仅仅是关于城市统计学的有趣实践。安吉尔先生毫不掩饰他的计划：他想要表明，人们涌入城市的脚步是不可能被阻止的；他认为，试图减缓甚至停止城市化进程不只会推高房价，还会造成各种各样不良的副作用 — 最终使穷人深受其害。举例来说，韩国的首都首尔，在1971年建立了一圈绿色保护带，到1990年，一户基本住宅的价格已经是一个普通人家全部收入的10倍。
Rather than copying such efforts to limit urban expansion, as some environmentalists advocate, rapidly growing cities in developing countries should take a page from New York and Barcelona, says Mr Angel. In the 19th century both cities decided to prepare themselves for rapid growth. In 1811 New York’s city council approved a plan which allowed all of Manhattan to be built up and included the island’s now famous street grid. In 1859 Barcelona followed suit with a similar concept to expand the city nine-fold.
与一些环保主义者的看法一样，安吉尔先生认为，与其采取这样的手段来限制城市扩张，发展中国家更应该向纽约和巴塞罗那学习。19世纪时这两个城市决定为快速扩张做准备。1811年，纽约议会批准了一项计划，允许建立曼哈顿区，这个小岛后来以出色的街区规划而闻名。1959年巴萨罗那也通过类似的计划使城市面积扩张了9倍。
Cities in developing countries must be equally ambitious if they want to be able to control the masses of people coming their way, says Mr Angel. They should plan for an arterial grid with roads no more than one kilometre apart and that covers an area big enough to accommodate newcomers for the next 20 to 30 years. And instead of surrounding the city with a greenbelt, they should protect sufficient open space within the city limits.
安吉尔先生说，发展中国家的城市要想控制住人口大量迁入，必须也具有类似的雄伟规划。他们必须规划建设主干路网，分支街道彼此距离不应超过一公里，覆盖面积要足够大，能够容纳未来20到30年进入城市的人口。他们不应该在城市周围架设绿色包围圈，而应该在有限的城市条件下保证足够多的露天场所。
Committed environmentalists and other defenders of urban containment are sure to reject at what Mr Angel calls “the making room paradigm”. But he makes a solid argument that this is a much more realistic way of dealing with urbanisation than building new city walls, particularly in developing countries. “As heroic and justified as it may be,” he writes, “containing the oncoming global urban expansion is much the same as holding back the tide.”
坚定的环保主义人士和其他主张限制城市发展的人肯定会反对安吉尔先生的“空间规划样板”。但安吉尔坚称与在城市周围建围墙相比，这才是实际可行的城市规划，在发展中国家中尤其如此。他写道：“虽然看上去很公平很了不起，但是想限制全球城市化进程，无异于像要阻止潮汐①一样异想天开。”
* “Planet of Cities”, by Shlomo Angel, Lincoln Institute of Land Policy, Cambridge, Massachusetts, 2012
“城市星球”，作者：什洛莫·安吉尔，林肯土地政策研究院，剑桥大学，马萨诸塞洲，2012
来自http://www.economist.com/blogs/freeexchange/2013/01/urbanisation
译注：①原文中的tide应该是双关语，tide本身有潮汐，潮流，趋势，时期的意思。意为：想要阻挡这种趋势，就像想要阻止潮起潮落一样是不可能的。
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