I downloaded your Population Grid maps for the United States and the World both at a resolution of 2.5 arc minutes, and I have a few questions. First, what are the units of the grid values? From what I've noticed, they run anywhere from the thousands to 1e-9, which seems kind of strange. Also, at the same resolution, why does the United States have more columns than the world?  The data at the top says there are 8688 columns at a cell size of 0.0416666, which would imply 362 longitudinal degrees of data.

There are three types of grids available from the GPW site with different units for each: population counts (persons), population densities (persons per square km), and areas (square kilometers). The range is very large for the population counts and densities as population is “spread” over grid cells, resulting in surfaces that vary from very high densities in urban areas to extremely low densities in large rural areas where less than a person per grid cell is common.

The tail part of the Aleutian Islands in Alaska crosses the date line into the eastern hemisphere. As a result of the data structure which splits the world at the date line, the grid for the United States spans the world east to west.  There may be additional cells outside of the date line at the edge for the United States, these can be safely ignored.


  1. I have imported the country-specific population density grid maps in ArcGIS for Argentina, Mexico and Honduras. I'm trying to join a table of points by latitude/longitude to these maps and export a table with all the data. The problem I'm having is that there does not seem to be any geographic data even though the maps are projected with WGS1984 correctly. I downloaded it from the site in the .bil format.
  2. I am using the GPW data (version 3) for China and I have some problems with understanding the proportional allocation mechanism. The reason that I am asking is that there are so many zeroes and I can not understand how there can be any zero?
  3. How do I convert .BIL format in Arcview/ArcInfo?
  4. How do I get GPW data into GRASS?
  5. How should I cite the GPW3 data?
  6. I am attempting to download and use your 1990 Adjusted Population Numbers for Africa. I have successfully downloaded the zipped BIL file. In order to convert this for use in my GIS software (I am using IDRISI) I need to know information which I cannot find in any of the documentation files you have made accessible. Please can you answer the following questions regarding the BIL format: 1. Is there a header - if so what is its size? 2. What are the maximum and minimum grid co-ordinates for your Africa data? 3. Are the data 8-bit or 16-bit? 4. What reference system do you use, and what the reference units measured in?
  7. I am having difficulties locating the metadata for your population density data of the world, GPWv3. Is the metadata available online?
  8. I am looking for gridded population data and elevation data on the same grid. I saw on your website that you have compiled a population dataset - is there an elevation dataset that can go with this, and can you help me obtain it?
  9. I am using the multibandread function in MATLAB to read in the glds95agi15.bil file I downloaded from CIESIN. I need help setting some of the input parameters for the function. * what is the height (rows), width (elements or columns), and depth (bands) of the file or how do I figure it out? * what is the number format? integer or float? how many bytes?
  10. I am very interested in the gridded population density data for Africa.The source for the maps you provide is cited as the UN, but having contacted them they are unsure of the data you have used to produce your maps.Is it possible to obtain these data from you, including population numbers for different regions of Africa as well as the density calculations that you have mapped?
  11. I downloaded the ArcInfo interchange files and tried (after import) to open them with the ARCGIS 8 software but each time it failed to open the file. I think the sta.adf file is missing (or another one). Could you please help me?
  12. I downloaded the global level data file v2glp95ag.zip I looked into the file content on a unix system using 'more', and found most grid values to be less than 1. This is unexpected, as I expected the number of inhabitants per cell. What did I do wrong?
  13. I downloaded the GPWv3 Population Density .ascii format. I'm having trouble parsing this data correctly. I read in the meta data at the top of the file (lower-left latitude/longitude origin of the grid, cell size, etc) and these seem to make sense. But when I plot all cells with a density greater than 300, the points are not syncing up with the map (i.e. I'm seeing large blobs of population in the Pacific). Am I correct in assuming that the rows of the file begin at the lower-left point given, with the columns representing increasing longitude and rows representing increasing latitude?
  14. I have been trying to download the GRUMP/GPW datasets but the web download does not seem to be working.
  15. I have downloaded India 1995 population data (GPW2). Why is there no variation in colours when I view the files in ArcView?
  16. I have successfully downloaded the GPW global datasets for the years 1990, 1995 and 2000. I would like to know if it is advisable to compare datasets of different years in order to assess changes in population densities and therefore migration patterns, or if there are constraints that hinder such operation.
  17. I plan to use the global population data. I would like to know what information is stored in the *.stx and *.blw files. Also is there a way to map the grids to (latitude, longitude) ?
  18. I would like to use the population estimates service, but don't know exactly how it works. I installed uDig with a WPS plugin, but I wonder which URL I have to use to connect to the sedac website.
  19. I'm using population density data, 2.5' grid.  My question is -- If a small populated island is the only land in a given cell, and its area is smaller than the cell's, how is the population density for the cell computed?  Is the population of the island distributed over the whole cell's area?  Or is the population density of the island applied to the whole cell?
  20. In GPW data that is comprised of 2.5 arc min cells, are the cells georeferenced from the cell center, or right/left and upper/lower corner?  I understand that xllcorner and yllcorner give the starting lat/lon for overall grid position, but are the cell data themselves valued at each lower left corner?
  21. In GPWv3 Population Density Grid data, .ASCII format, what is the definition of "xllcorner" and "yllcorner" values?
  22. In GPWv3, how do you consider the population density in a bin (0.25 deg x 0.25 deg) when it is partly landmass and partly water (e.g., sea, ocean)? Do you evaluate the density as the total number of humans over the total surface of this bin (so, approximately, let's say 30 km x 30 km, even if depending on latitude) or just only over the landmass part?
  23. In GPWv3, what exactly does "No Data" (-9999) mean?
  24. In UN-adjusted 2000 density data, how is the data adjusted to match UN totals ? The Africa UN-adjusted map shows some significant chunks of zero density (e.g, much of Gabon) that don't seem realistic.
  25. I downloaded your Population Grid maps for the United States and the World both at a resolution of 2.5 arc minutes, and I have a few questions. First, what are the units of the grid values? From what I've noticed, they run anywhere from the thousands to 1e-9, which seems kind of strange. Also, at the same resolution, why does the United States have more columns than the world?  The data at the top says there are 8688 columns at a cell size of 0.0416666, which would imply 362 longitudinal degrees of data.
  26. My question is about the grid pixel, is the grid center of the pixel or not? I mean, if the latitude begins from 5° and longitude from 65°, is (65,5) the center or one edge of pixel?
  27. Regarding the uniform field of values that fill each population subregion, my hope when I downloaded the 2.5 minute GPWv3 population grid (95ag) file was that they would indicate the population in that 2.5 minute cell, since the documentation refers to 2.5 minute resolution. However, I suspect that they actually represent the sum of the population in the total area of the subregion. What do the values in each cell actually represent?
  28. The maps on the GPW web site report population in the thousands.  Is this the same for the grid or is it unscaled?
  29. We are looking for a high-resolution gridded population data for our project.  It seems to us that compared to the GWP3 data, the GRUMP data offer a higher spatial detail and probably a more accurate spatial distribution of population.  Which would you recommend ?
  30. We have been using the GPW data extensively, but one question I cannot understand is why the data appear not to be available in database format rather than GIS format.
  31. What are the differences between GPW, GRUMP and Landscan?
  32. What are the restrictions on use and redissemination of data?
  33. What has happened to .e00 format option? It appears to have been replaced by something called "grid"?
  34. What is a .BIL image file format?
  35. What is the difference between "..ag"  and "...g" files?  For example, I've downloaded the population grid for the whole world for 1990, in "grid" format, and there are two sets of raster files.  When I open them in ArcGIS, they seem to show similar data, but the range of values for the raster is somewhat different: 0 to 1.24 million versus 1 to 1.17 million.
  36. What is the difference between GPW and GRUMP population grids?
  37. What is the projection used for the data?
  38. What years are the data available for?
  39. 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?
  40. Which are the last updated and the next scheduled GPW collected data?
  41. Why can't I make the Import71 work with the GPW data?
  42. Why is there a difference between the population estimates of UN and National Statistical Offices estimates?
  43. Is the data symmetrical from the Equator?  In the ascii format using a 0.5 degree resolution, the yllcorner equals -58 degrees. Since there are 286 rows, this represents a total of 143 degrees. Is the upper left corner then at 85 degrees latitude (-58 + 143)?

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