1. What is the most recent Revision of World
Urbanization Prospects?


The 2014 Revision is the most recent revision of World Urbanization Prospects which are the official United Nations estimates and projections of rural and urban population as well as urban agglomerations. Please note that the next round of World Urbanization Prospects will be released in the year 2018.



2. How do we estimate the proportion urban and
rural for each country?


The proportion of urban (and rural) population is
estimated from the most recently available census or official population
estimate of each country. If this estimate is only available for some period
in the past, the proportion urban is extrapolated to the base year. In the 2014
Revision of the World Urbanization Prospects the base year is 2014.



3. How do we define "urban"?


We do not use our own definition of
"urban" population but follow the definition that is used in each
country. The definitions are generally those used by national statistical
offices in carrying out the latest available census. When the definition used
in the latest census was not the same as in previous censuses, the data were
adjusted whenever possible so as to maintain consistency. In cases where
adjustments were made, that information is included in the sources listed
online. United Nations estimates and projections are based, to the extent
possible, on actual enumerations. In some cases, however, it was necessary to
incorporate other estimates of urban population size. When that is done, the
sources of data indicate it.



4. How do we define "urban
agglomeration"


The term “urban agglomeration” refers to the
population contained within the contours of a contiguous territory inhabited
at urban density levels without regard to administrative boundaries. It
usually incorporates the population in a city or town plus that in the
suburban areas lying outside of, but being adjacent to, the city boundaries.
Whenever possible, data classified according to the concept of urban
agglomeration are used. However, some countries do not produce data according
to the concept of urban agglomeration but use instead that of metropolitan
area or city proper. If possible, such data are adjusted to conform to the
concept urban agglomeration. When sufficient information is not available to
permit such an adjustment, data based on the concept of city proper or
metropolitan area are used.



5. What methods are used to project the urban
population?


We are using an established and robust
extrapolation method to project the urban population for the World
Urbanization Prospects. The method is based on the urbanrural ratio,
which we calculate for the last two empirical data points available  which
are typically based on results from two censuses. The urbanrural ratio is
directly related to the percentage urban. The calculations are done in two
steps:


●
First, we calculate the average annual rate of change in the urbanrural
ratio between the last two data points. For instance, we might have census
results for 2000 and 2010 for a particular country, which indicate that the
urbanrural ratio in 2000 was 30/70 and the urban rural ratio in 2010 was
35/65. From these two data points we can calculate an average annual rate of
change in the urbanrural ratio for the 2000 to 2010 period. This rate is
equivalent to the difference between the rate of change of urban population
and the rate of change of the rural population. This rate of change is
then extrapolated, assuming that the proportion urban follows a logistic
path.


● In
a second step we apply what we call the “world norm”. This global norm
combines empirical urbanrural growth differences from 148 countries with 2
million or more inhabitants in a regression equation. The fitted regression
line allows us to calculate a “hypothetical urbanrural growth difference”
for each level of an initial observed percentage urban. We can now use
the most recent urbanrural growth difference of a particular country
(obtained in step 1) and converge it to the hypothetical urbanrural
growth difference of all countries of the world (obtained in step 2) over a
period of 25 years.



With this procedure, we essentially allow the
urbanization process of a particular country to converge towards a worldwide
observed pattern of urbanization. (In technical terms: the urbanrural
growth differences are not kept constant over the projection period, but
converge towards the hypothetical urbanrural growth difference for all
countries of the world with 2 million or more inhabitants).
