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    1. GPWv4 releases data for five years: 2000, 2005, 2010, 2015, 2020. Is it advisable to compare data sets of different years in order to assess changes in population density over time? Are there constraints in using the GPWv4 target year data sets as a time series?

    2. For which part of the earth's land surface is the human footprint data available?

    3. I am looking for projection information for your Mexican Municipios data. I need to reproject the data and I need to know what the original projection was for the coverage.

    4. How is SEDAC’s Gridded Species data different than the IUCN Red List?

    5. 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.

    6. What does a zero in the population density grid mean? What does No Data mean?

    7. What were the data sources used for the 2001 ESI?

    8. What are the restrictions on use and redissemination of data?

    9. 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?

    10. Which ellipsoid / spheroid is the geographical data of the Fundamental GIS: Digital Chart of China based on?

    11. I see you have data on mammals and amphibians, do you also have richness grids for bird species?

    12. I have a question regarding the data set Contours of China and the Surrounding Areas. What Surrounding Areas are included in the data? What is the difference between the contour.zip file and the contourp.zip?

    13. 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.

    14. 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?

    15. Do the RDS data sets (which are matched to these points) contain different information from the raster grids (GeoTiff?).

    16. 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 ?

    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. 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?

    19. Where can I find land area data for 1990 census tracts? I am trying to determine the median square mileage of census tracts.

    20. I am having difficulties locating the metadata for your population density data of the world, GPWv3. Is the metadata available online?

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