What are the differences between GPW, GRUMP and Landscan?

Gridded Population of the World (GPW) version 3 is based on 2000 round census data. In addition to a year 2000 grid, it includes 1990 and 1995 grids (based on 1990 round census data and interpolations between 1990 and 2000 round censuses), and projected 2005, 2010, and 2015 grids. These represent continuations of the 1990-2000 population trends, with pixel estimates based on a projection of the trend but capped so that the national level totals do not exceed UN projections. GPW is at a 2.5 minute resolution (approximately 5km at the equator), and a derivative product, Global Rural-Urban Mapping Project (GRUMP) v.1, is at a 30 arc-second (1km) resolution (the same as Landscan), and includes an urban-rural reallocation. GRUMP has 1990, 1995, and 2000 population grids.

The following represents a comparison with Landscan 2009

- Landscan represents daytime “ambient” population, whereas GPW represents night-time population. Depending on the application, this distinction may be important. For example, disaster evacuation plans would need to take into account where the population is at a given time, and exposures to environmental pollutants such as day-time smog or night-time heat island effects, will require different data.

- Landscan is a modeled data set. The data set creators apply multi-layered, dasymetric, spatial modeling approach to reallocate populations based on layers representing land use/land cover,  high resolution imagery analysis, transportation networks, elevation, slope, etc. The precise reallocation algorithm is not documented. GRUMP is a “lightly modeled” data set with an urban reallocation based on a night-time lights data layer.  GPW does not model or reallocate the population, but simply grids data based on the original census units, at the highest spatial resolution (smallest spatial size) for which they are available by country. For applications in which the independent variable is anyone of these layers used in Landscan or GRUMP, users are advised to use GPW, since these variables are exogenous to GPW.  

- Landscan has annual updates, but owing to budgetary constraints, CIESIN and its partners only produce  a new version of GPW following each decadal census round. Earlier Landscan releases may not be consistent with current releases owing to changes in data sources and methods. CIESIN’s GPWv3 has consistent time series for each five year interval from 1990-2015 based on census data from the 1990 and 2000 census rounds.

- Globally, Landscan uses 8,285,172  census inputs, whereas GPW v.3 uses 399,747units. The Landscan number is large because of the way the USA is processed (Ambient Global data is processed using LandScan USA Night/Day inputs). Outside the USA Landscan used 79,590 administrative units for ambient modeling. By contrast,  GPWv3 uses  338,863 units outside of the US. Country-by-country details are all in a spreadsheet available at: http://sedac.ciesin.columbia.edu/gpw/spreadsheets/GPW3_GRUMP_SummaryInformation_Oct05prod.xls.

- GPW is free of charge whereas commercial users of Landscan are charged a fee to use the data.

Further documentation on GPW v3 and GRUMP is available from http://sedac.ciesin.columbia.edu/gpw/documentation.jsp, and further documentation on Landscan is available through the Documentation and FAQ pages at http://www.ornl.gov/sci/landscan/

GRUMP

  1. After extracting all the data from GRUMP and adding up population by country to get country population totals, should the totals add up to match exactly the totals reported in the country summary?
  2. Are the quadrilaterals formed by the meridians and parallels of the Urban/Rural Area grids proportional to the area on the globe?
  3. How big is the file (.ascii) of GRUMP data? I am downloading from a very fast connection and it is still taking a really long time.
  4. I am looking for the population and the surface area (in square kilometers) for several cities throughout the globe.  I found several datasets available in GRUMP, but I didn't find anything with both population and surface area.
  5. I am slightly confused as to what is meant by "urban extent" and "settlement points" - please could you send me a definition? Also, I have found the global map which shows "urban extent" - which I guess is the areas of the Earth's surface which are covered by urban areas. I am wondering if you, or anyone else you know of, has a time-series of such maps, showing how urban coverage has changed over time?
  6. I am trying to get population densities for world metropolitan areas (e.g., # of residents per square kilometer or square mile) and if possible comparison figures for previously points in time (e.g., the latest available estimate versus 1 year ago, 5 years ago, etc.).  Can I use the GRUMP data ?
  7. I compared GRUMP Alpha population grid and GPW v3 population grid for the year 2000 in 1° grid. I am surprised to see that there are some huge differences (the largest difference that I noticed is 8.77x106 people).  How do you explain these huge differences?
  8. I download GRUMP 2000 population count data set. It sees that maximum population count is 1,346,772 in the cell of that data set. I would like to know that is right or not, because I think that the value is very large. Could you give me advice about maximum population count in GRUMP?
  9. I downloaded GRUMPv1's Population density. From the metadata associated with the files I understand that each cell/pixel is the average population density in units of person per sq km. When I zoomed in to Chicago, IL and NY there appear to be a suite of pixels with population densities greater than 20,000 people per sq km which seems off by a factor of 10. Would you mind confirming those values.
  10. I downloaded the urban extents grid from GRUMP (alpha).  When opened in ArcGIS, there are only two values 1 and 2.  What do these values mean ?
  11. I have been trying to download the GRUMP/GPW datasets but the web download does not seem to be working.
  12. I need some gridded population information so I downloaded GRUMPv1, which seems like it should be perfect for my needs. However the number in the file naup00g.asc (North America unadjusted population counts in the grid) are small floating point numbers. I had expected that they would be population counts in the grid cell, which is what the documentation seems to say. Not sure how to interpret values like "2.35144e-005" as a population count! Am I misinterpreting these somehow?
  13. I would like to download GPW and GRUMP data, but I'd like to know if it is possible to download files by some coordinate extent, rather than by country?
  14. In the Urban extents data, how were the urban areas identified?
  15. I’ve downloaded the GRUMP 30 arc-second area grid (ASCII format), and am confused by the units. The meta data says that the units are km2 of land area, but when I unzip the file (using gunzip), producing gluareag_alpha1.asc, then the land cells have values of 56 (or less, if not completely land). Also, the missing value should be -9999 but the data file has 0 instead.
  16. There is a slight misalignment between the pop density and the urban extent data layers for Africa, due to differences in the BLW files. The former layer has 0.00833333333330 0.00000000000000 0.00000000000000<br/><br/> -0.00833333333330 -25.99583333333335 37.99583333303735<br/><br/>and the latter has<br/><br/> 0.00833333000000<br/><br/> 0.00000000000000<br/><br/> 0.00000000000000<br/><br/> -0.00833333000000<br/><br/> -25.99583333500000<br/><br/> 37.99580373499999<br/><br/> <br/><br/>This makes a difference of a couple of hundred meters. Is this just because the analysts were rounding? Is it okay to use the same BLW data for both files?
  17. We are looking for a high-resolution gridded population data for our project. It seems to us that compared to the GPW3 data, the GRUMP data offer a higher spatial detail and probably a more accurate spatial distribution of population. Which would you recommend ?
  18. What are the differences between GPW, GRUMP and Landscan?
  19. What are the restrictions on use and redissemination of data?
  20. What is the difference between GPW and GRUMP population grids?
  21. What is the exact spatial domain of the .asc urban extent grid? Is it from -56.0 to +84.0 *included*?
  22. What is the spatial extent domain for the different file formats of 30" GRUMPv1 Urban Extent Grid?
  23. Where are the attribute tables for the GPWv3/GRUMP data? I would eventually like to extract statistics (such as population count) using features in another layer, but am not sure that I'll be able to do so given that there are no accompanying attribute tables. Could you advise as to how I should proceed?
  24. Why is it that the total population of the settlement points is not equal to the country total population?

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