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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.
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Since the footprint data uses the spheroid GRS1980, can I just define it as NAD1983? I know that NAD1983 uses GRS1980, but I am not sure if I can define this layer as datum-based instead of spheroid-based.
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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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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 ?
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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
-0.00833333333330 -25.99583333333335 37.99583333303735
and the latter has
0.00833333000000
0.00000000000000
0.00000000000000
-0.00833333000000
-25.99583333500000
37.99580373499999
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? -
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?
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We have downloaded the population estimate data for France (frap05ag.asc). When we use this file to calculate population for a given polygon, it does not match the response returned by the Population Estimation Service provided. We were wondering what is your criteria for including a grid cell in the calculation? Are you giving weight to a cell based on polygon intersection area? Also, wanted to clarify the xll, yll corner values - do the values -6, 40 represent the center of the bottom left cell or do they represent bottom left corner of the bottom left cell?