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    1. Is there any way to find out how block groups from the 1990 census match with block groups from the 1980 census? I need to find or create data that would show the change in block group characteristics over time. I tried MABLE but it only has block group information for 1990 census.

    2. In the China County-level Data on Provincial Economic Yearbooks, each of the DBF files has its meaning, such as 1990B1.dbf is about the General Survey. But when I open the file, all the item names are given as sequential number codes, such as B1990001, B1990002, B1990003. I want to know about each item's name -- what's the value meaning?

    3. 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?

    4. 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?

    5. What types of crops were included in the study?

    6. 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?

    7. 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.

    8. I would like to do a time series analysis to look at the change in environmental sustainability in specific countries, but I am unsure if the data for your 2001 and 2002 ESI is different, or whether the 2002 ESI is just the result of fine-tuning definitions and categories.

    9. 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.

    10. 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?

    11. 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?

    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. What are the advantages of GPW over other products?

    14. What is the User Registration System and why do I have to register?

    15. What are the differences between GPW, GRUMP and Landscan?

    16. Where is aerosol optical depth on the app?

    17. When will the rasters of census variables (sex, age, and urban/rural designation) be released?

    18. What is the difference between the Water Mask layer and the Water Area layer?

    19. Can I assemble the releases of the EPI into a time series or panel dataset?

    20. I am working on a map of Mexico that details population dynamics at the state level and am wondering if you have such information (e.g., total fertility rate, natural increase, inward and outward migration), or if you have a suggestion as to who I might contact.

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