The UN Population Division Urban Database

Transcription

1 The UN Urban Database World Urbanization Data An overview of World Urbanization Prospects [WUP] UN

2 History of WUP No. Assessment Period Remarks Urban rural populations Urban agglomerations Extended to 2050 (? ) UN

3 Objectives of WUP Provide a comprehensive account of basic indicators of urbanization for all countries the world. Focus on two indicators: Proportion urban population of urban locations (urban agglomerations). UN

4 Coverage: Urban Rural s Captured as proportion Urban for 228 countries or areas, from China to Pitcairn. Calculation of urban rural population based on estimates projections of total population from current Revision of World Prospects. UN

5 Coverage: Urban Rural s Observed data points in database: 1,907. Observed data points used for estimates projections: 1,667 UN

6 Coverage: Urban Rural s Frequency of observed data: Proportion Urban 100 Number of observed data UN

7 Coverage: Urban Rural s Estimates projections for for 228 countries Published estimates projections for for 228 countries UN

8 Coverage: City s City population data for 4,259 urban locations in 228 countries Observed data points in database: 27,174. Observed data points directly used for estimates projections: 23,956 UN

9 Coverage: City s Frequency of observed data: of urban locations data Number of observed UN

10 Coverage: City s Distribution of Urban Locations by Size Class 2,500 Number of urban locations 2,000 1,500 1, <5,000 5,000-50,000 50, , , , ,000-1,000, Mio 5-10 Mio 10 Mio+ Size class UN

11 Coverage: City s Urban location in database Size class Frequency Cumulative % <5, % 5,000-50, % 50, , % 100, ,000 2, % 500,000-1,000, % 1-5 Mio % 5-10 Mio % 10 Mio % UN

12 Coverage: City s Estimates projections for for 4,259 urban locations: 23,956 data points (internal). Published city populations for urban locations with 750,000 inhabitants or more for : 568 urban locations UN

13 Coverage: City s Year City population Urban Coverage population All cities Publ. cities All Published ,792, ,165, ,764,838 84% 46% ,251, ,882, ,436,181 82% 46% ,066, ,379, ,353,043 81% 46% ,457, ,004,580 1,157,715,037 79% 45% ,041,879, ,900,549 1,328,846,686 78% 46% ,170,898, ,056,621 1,515,869,535 77% 46% ,315,232, ,309,498 1,736,301,572 76% 45% ,458,190, ,926,998 1,983,674,071 74% 44% ,623,852, ,742,977 2,270,869,202 72% 43% ,790,122,829 1,092,850,900 2,551,364,022 70% 43% ,977,794,404 1,221,610,868 2,844,801,880 70% 43% ,172,683,571 1,344,486,874 3,150,450,636 69% 43% ,369,994,797 1,465,751,630 3,474,570,657 68% 42% ,565,702,369 1,583,322,420 3,819,022,892 67% 41% ,757,845,468 4,177,105,794 66% ,943,610,959 4,542,365,861 65% ,122,398,851 4,912,553,004 64% UN

14 Track record 1 Projecting 50% urban: World Year at which 50% urba an was expected Revision UN

15 Track record 2 Projecting 50% urban: LDR was expected Year at which 50% urban Revision UN

16 Logical data model The WUP database documents for each data point: The data generating process [Census, survey, etc] The statistical concept [de-jure, de-facto] The data status [preliminary, final] The data reliability [high, questionable] Source of data [Title, organization year, comment]. UN

17 ProUrban software UN

18 ProUrban software UN

19 Procedures Collecting estimating urban populations from a variety of sources Mapping national definitions into three generic categories: City proper, urban agglomeration, metropolitan areas. Identification documentation of urban locations in local language or established/documented transliteration [Roma, not Rome]. UN

20 Constraints Current project relies on national definitions for defining urban areas urban locations. Focus on (large) urban agglomerations leaves the most dynamic part of the urbanization process out of the picture UN

21 Estimation projection methodology Modeling the envelope: proportion urban Consistency enforced by a global norm of the urban-rural growth differential. Preliminary analysis suggests that the current 25 year transition period from observed values to global norm is too short. UN

22 Procedures/Methodology Projecting populations in urban locations in a two stage process: First independent growth (including consistency constraint by global norm) Correction of urban location population growth exceeding the urban population (the envelope) UN

23 Constraints limitations Difficult to capture population decline estimates projections from UN

24 Constraints limitations But global growth rates already declining since late % 2.0% 1.5% 1.0% estimates projections from % 0.0% -0.5% -1.0% UN

25 Constraints limitations No account of uncertainty (no variants) No provision of hierarchy of urban locations [city proper => Urban agglomeration => Metropolitan area] No account for physical or natural limits (space, environment) UN

26 Constraints limitations No provision for the birth of new cities (see Krugman). The occurrence of new locations is registered in past estimates, but the projection algorithm does not account for it. Modeling as a single pulse, unidirectional diffusion process UN

27 Constraints limitations Dependence on national definitions of urban areas urban locations Criterion Countries Administrative 83 Economic 1 size 57 Urban characteristic 4 Any combination 48 Entire population 6 No urban population 3 Unclear definition No definition 1 25 Total 228 UN

28 WUP 2007 Identifying the location of cities (Centroids) Extension of projection horizon (2050?) Lowering the threshold for publication to 100,000 inhabitants UN

29 Beware: Forecasting In the Inferno of Dante s Divine Comedy, a special place in the Eight Circle of Hell is reserved for those who peer to far into the future. The Poet relates the punishment of such as presumed, while living, to predict future events. It is to have their faces reversed set the contrary way on their limbs, so that, being deprived of the power to see before them, they are constrained ever to walk backward UN